PHYSICSWIKI:Manual of Style/Dates and numbers

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This part of the Manual of Style helps editors to achieve consistency in the use and formatting of numbers, dates, times, measurements, currencies, and coordinates in PhysicsWiki articles. Consistency in style and formatting promotes clarity and cohesion; this is especially important within an article. The goal is to make the whole encyclopedia easier and more intuitive to use. Try to write so the text cannot be misunderstood, and take account of what is likely to be familiar to readers—the less they have to look up definitions, the easier it is to be understood.

Where this manual provides options, consistency should be maintained within an article unless there is a good reason to do otherwise. In direct quotations, the original text should be preserved. The Arbitration Committee has ruled that editors should not change an article from one guideline-defined style to another without a substantial reason unrelated to mere choice of style, and that revert-warring over optional styles is unacceptable.[1] If discussion cannot determine which style to use in an article, defer to the style used by the first major contributor.

Non-breaking spaces

Chronological items

Precise language

Avoid statements that date quickly, except on pages like current events that are updated regularly. Avoid words such as now, soon or in modern times (unless their intended meaning is clear), currently and recently (except on rare occasions where they are not redundant), or phrases such as the sixties. Instead, when writing about past events use more precise phrases such as during the 1990s or in August 1969. For future and current events, use phrases such as as of December 2017 or since the beginning of 2010 that indicate the time-dependence of the information to the reader. Relative time words are acceptable when very long periods, such as geological epochs, are considered: Our ancestors are believed to have diverged from the other great apes long ago, but only recently developed the use of fire.

To help editors keep information up to date, statements about current and future events may be used with the as of technique. This is done by using the {{as of}} template to tag information that may become dated quickly: {{as of|2017}} produces the text As of 2017 and categorises the article appropriately. This technique is not an alternative to using precise language. For instance, one should not replace since the start of 2005 with {{as of|2005}} because some information (the start of 2005) would be lost; instead, use either the plain text or a more advanced feature of {{as of}} such as {{as of|2005|alt=since the start of 2005}}.

Before saving an edited passage, it is useful to re-read that passage from the perspective of a reader five years in the future.

Time of day

Context determines whether the 12- or 24-hour clock is used; in both, colons separate hours, minutes and seconds (e.g. 1:38:09 pm or 13:38:09).

  • 12-hour clock times end with dotted or undotted lower-case a.m. or p.m., or am or pm, preceded by a space (e.g. 2:30 p.m. or 2:30 pm, not 2:30p.m. or 2:30pm). Hours denoted by a single digit should not have a leading zero (e.g. 2:30 p.m., not 02:30 p.m.). A hard space (see above) is advisable (2:30 pm or {{nowrap|2:30 p.m.}}). Use noon and midnight rather than 12 pm and 12 am; whether midnight refers to the start or the end of a date will need to be specified unless it is clear from the context.
  • 24-hour clock times have no a.m., p.m., noon or midnight suffix. Hours under 10 should have a leading zero (e.g. 08:15). 00:00 refers to midnight at the start of a date, 12:00 to noon, and 24:00 to midnight at the end of a date, but should not be used for the first hour of the next day (e.g. use 00:10 for ten minutes after midnight, not 24:10).

Time of day is normally expressed in figures rather than being spelled out. For details, and information on time intervals (e.g. 5 minutes), see Numbers as figures or words, below.

Day, month and season names

See PhysicsWiki:Manual of Style/Capital letters#Calendar items

Dates

Acceptable date formats

The following date styles are acceptable in PhysicsWiki articles, subject to rules included thereafter:

Format Example Scope
D MMMM YYYY
Numeric day, space, full month name, space, full year
8 September 2001 Everywhere
MMMM D, YYYY
Full month name, space, numeric day, comma, space, full year
September 8, 2001
D MMM YYYY
Numeric day, space, short month name, space, full year
8 Sep 2001 Only in references, tables, lists or areas where conciseness is needed (Please see: PhysicsWiki:Citing Sources § Citation style)
MMM D, YYYY
Short month name, space, numeric day, comma, space, full year
Sep 8, 2001
YYYY-MM-DD
Four-digit year, hyphen, two-digit month, hyphen, two-digit day
2001-09-08
  • Year-initial numerical (YYYY-MM-DD) dates (e.g. 1976-05-31) are uncommon in English prose, and should not be used within the article body. However, they may be useful in long lists and tables for conciseness. Because year-initial dates might be assumed to follow the ISO 8601 standard, which mandates the Gregorian calendar, this format should only be used for dates expressed in the Gregorian calendar and for the years 1583 through 9999.
  • For sorting in tables see Date sorting problems or consider using {{sort|2008-11-01|1 Nov 2008}} or {{dts|Nov 1, 2008}}.
  • If a date range is abbreviated, use the formats 5–7 January 1979 or January 5–7, 1979 with an unspaced en dash. An unspaced en dash is also used for month or year ranges, such as June–August 1940 or the 1939–45 war. However, between two months and days, use a spaced en dash, such as June 3 – August 18 or June 3, 1888 – August 18, 1940. The space before an en dash should preferably be a non-breaking space ( ).
  • A night may be expressed in terms of the two contiguous dates using a slash (the bombing raids of the night of 30/31 May 1942).

Unacceptable date formats

The following date styles are not acceptable in PhysicsWiki except in external titles and quotes:

  • PhysicsWiki does not use ordinal suffixes, articles, or leading zeros (except for the YYYY-MM-DD format). PhysicsWiki does not insert a comma between month and year, nor does it insert a full stop after the day (10 June 1921); however, when using the mdy format, a comma is required between day and year. When a date in mdy format appears in the middle of text, include a comma after the year (The weather on September 11, 2001, was clear and warm). Write out the full year string instead of using the apostrophe (') to abbreviate the first two digits of the year.
Incorrect Correct
9th June
the 9th of June
9. June
9 June
June 9th June 9
June, 2001 June 2001
9 June, 2001
09 June 2001
9 June 2001
June 9 2001
June 09, 2001
June 9, 2001
'01 2001
  • An exception to this guideline is when a specific style of a date achieves notability within a culture, such as the Fourth of July (does not adhere to ordinal nor spelled out guideline, yet is acceptable).
  • Do not use year-final numerical date formats (DD/MM/YYYY or MM/DD/YYYY), as they are ambiguous: "03/04/2005" could refer to 3 April or to March 4. For consistency, do not use such formats even if the day number is greater than 12.
  • Do not use customized variations of the YYYY-MM-DD format. E.g., do not replace hyphen characters ("-") with any other character; do not change the order of year, month, or day. Use leading zeros for days or months when needed to make these fields two digits.
  • Yearless dates (5 March, March 5) are inappropriate unless the year is obvious from the context. There is no such ambiguity with recurring dates, such as January 1 is New Year's Day.
  • Do not use Roman numerals, such as "MMXII" for "2012", to denote years.

Consistency

  • Dates in article body text should all have the same format:
  • Correct: Julia ate a poisoned apple on 25 June 2005. She died three days later on 28 June.
  • Incorrect: Julia ate a poisoned apple on 25 June 2005. She died three days later on June 28.
  • Publication dates in article references should all have the same format. Although nearly any consistent style may be used, avoid all-numeric date formats other than YYYY-MM-DD.
For example, in the same article, write
  • Jones, J. (20 Sep 2008)
  • Smith, J. (Sep 2002)

but not
  • Jones, J. (20 Sep 2008)
  • Smith, J. (September 2002)

  • Access and archive dates in references should all have the same format – either the format used for publication dates, or YYYY-MM-DD.
For example, in the same article, write
  • Jones, J. (20 Sep 2008) ... Retrieved 5 Feb 2009.

or
  • Jones, J. (20 Sep 2008) ... Retrieved 2009-02-05.

but not
  • Jones, J. (20 Sep 2008) ... Retrieved 5 February 2009.
  • Jones, J. (20 Sep 2008) ... Retrieved Feb 5, 2009.
  • Jones, J. (20 Sep 2008) ... Retrieved February 5, 2009.

  • These requirements do not apply to dates in quotations or titles.
  • Date formats in quotations or titles should not be changed, even if this causes inconsistent formats in the same article.
  • It is acceptable to change other date formats in the same article to provide consistency, so long as those changes would otherwise be acceptable.

See: {{Use dmy dates}}, {{Use mdy dates}}

Strong national ties to a topic

  • Articles on topics with strong ties to a particular English-speaking country should generally use the more common date format for that nation. For the United States, this is month before day; for most others, it is day before month. Articles related to Canada may use either format consistently.
  • Sometimes the customary format differs from the usual national one: for example, articles on the modern US military use day before month, in accordance with military usage.
  • YYYY-MM-DD format may be used in references or in tables, even in articles with national ties, if otherwise acceptable.

Retaining the existing format

  • If an article has evolved using predominantly one format, the whole article should conform to it, unless there are reasons for changing it based on strong national ties to the topic or consensus on article talk.
  • The date format chosen by the first major contributor in the early stages of an article should continue to be used, unless there is reason to change it based on strong national ties to the topic or consensus on article talk.
  • Where an article has shown no clear sign of which format is used, the first person to insert a date is equivalent to "the first major contributor".

Dates of birth and death

Dates of birth and death are provided in articles on people, generally at the start of articles. For example: "Charles Robert Darwin FRS (12 February 1809 – 19 April 1882) was an English naturalist ..." The two dates are separated by an en dash (HTML code: –). When either date contains a space, the en dash is preceded by a space (preferably a non-breaking space, code:  ) and followed by a space (see MOS:ENDASH).

  • For an individual still living: "Serena Williams (born September 26, 1981) ...", not "... (September 26, 1981 –) ..." nor "... (born on September 26, 1981) ..."
  • When only the years are known: "Socrates (470–399 BC) was..." The year of death is given in full: "Petrarch (1304–1374) was ...", not "... (1304–74) was ..."
  • When the year of birth is completely unknown, it should be extrapolated from earliest known period of activity: "Offa of Mercia (before 734 – 26 July 796) ..."
  • When the year of birth is known only approximately, use {{circa}}: "John Sayer (c. 1750 – 2 October 1818) ..."
  • When a date is known to be one of two years (e.g. from a regnal or AH year conversion, or a known age at death), use this format: "Anne Smith (born 1912 or 1913; died 2013) ..."
  • When the years of both birth and death are known only approximately: "Dionysius Exiguus (c. 470 – c. 540) ..."
  • When the date of death is completely unknown, it should be extrapolated from last known period of activity: "Robert Menli Lyon (1789 – after 1863) ..."
  • When the reign of a sovereign is uncertain: "Rameses III (reigned c. 1180 BCE – c. 1150 BCE) ..."
  • When the individual is known to have been alive (flourishing) at certain dates, [[floruit|fl.]] or {{fl.}} is used in articles, not disambiguation pages, to link to floruit, in case the meaning is not familiar: "Osmund (760–772fl. 760–772) ..."
  • When the individual is known to have been alive as early as about 660, and to have died in 685: "Aethelwalh (c. 660 – 685fl. c. 660 – 685) ..."

In biographical infobox templates, provide age calculation and microformat compatibility with date mathematics templates. See the documentation for those templates to learn how to use them, and PhysicsWiki:Manual of Style/Biographies for more guidelines on articles about people.

Other date ranges

Dates that are given as ranges should follow the same patterns as given above for birth and death dates.

<span id="Date autoformatting" /> Linking and autoformatting of dates

Dates should not be linked purely for the purpose of autoformatting (even though linking was previously recommended).[2] Dates should only be linked when they are germane and topical to the subject, as discussed at PhysicsWiki:Linking#Chronological items.

Longer periods

  • Months are expressed as whole words (February, not 2), except in the YYYY-MM-DD format. Unlike some other languages, the names of months and days of the week are capitalised in English. Abbreviations such as Feb. in the United States or Feb in most other countries are used only where space is extremely limited, such as in tables and infoboxes. Do not insert of, or a comma, between a month and a year (April 2000, not April of 2000 or April, 2000).
  • Seasons. As the seasons are reversed in the northern and southern hemispheres—and areas near the equator tend to have just wet and dry seasons—neutral wording (in early 1990, in the second quarter of 2003, around September) is usually preferable to a "seasonal" reference (summer 1918, spring 1995). Even when the season reference is unambiguous (as when a particular location is clearly involved) a date or month may be preferable to a season name, unless there is a logical connection (the autumn harvest). Season names are preferable, however, when they refer to a phase of the natural yearly cycle (migration to higher latitudes typically starts in mid-spring). Seasons are normally spelled uncapitalized.
  • Years
    • Years are normally expressed as digits. Avoid inserting the words the year before the digits (1995, not the year 1995), unless the meaning would otherwise be unclear.
    • Year ranges, like all ranges, are normally separated by an en dash, not a hyphen or slash: 2005–06 (unspaced) generally denotes a two-year range; 2005/06 may be used to signify a period of 12 or fewer months, such as a corporate or governmental fiscal year, if that is the convention used in reliable sources; sports seasons spanning two calendar years should be uniformly written as 2005–06 season.
    • A closing CE or AD year is normally written with two digits (1881–86) unless it is in a different century from that of the opening year, in which case the full closing year is given (1881–1986). For clarity, years with fewer than four digits may be written in full (355–372).
    • A closing BCE or BC year is given in full (2590–2550 BCE). While one era signifier at the end of a date range requires an unspaced en dash (12–5 BC), a spaced en dash is required when a signifier is used after the opening and closing years (5 BC – AD 29).
    • Ranges expressed using prepositions (from 1881 to 1886 or between 1881 and 1886) should not use en dashes (not from 1881–86 or between 1881–86).
    • To indicate around, approximately, or about, the unitalicised abbreviation c. is preferred over circa, ca, ca., approximately, or approx., and should be spaced (c. 1291). Do not use a question mark for this function (1291?), as this may imply to the reader an uncertainty on the part of PhysicsWiki editors rather than on the part of reliable historians.
  • Decades
    • Decades as such contain neither an apostrophe nor the suffix -ies (the 1980s, not the 1980's, not the 1980-ies, and definitely not the 1980s'). The two-digit form is never used in reference to the decade as a time span per se.
    • The two-digit form, to which a preceding apostrophe should be added, is used only in reference to a social era or cultural phenomenon that roughly corresponds to and is said to define a decade, and only if it is used in a sourceable stock phrase (the Roaring '20s, the Gay '90s), or when there is a notable connection between the period and what is being discussed in the sentence (a sense of social justice informed by '60s counterculture, but grew up in 1960s Boston, moving to Dallas in 1971). Such an abbreviation should not be used if it would be redundant ('80s Reaganomics) or if it does not have a clear cultural significance and usage (the '10s).
  • Centuries and millennia
    • For purposes of written style, PhysicsWiki does not recognise a year 0. Therefore, for dates AD (or CE) the 1st century was 1–100, the 17th century was 1601–1700, and the second millennium was 1001–2000; for dates BC (or BCE) the 1st century was 100–1; the 17th century was 1700–1601, and the second millennium was 2000–1001.
    • Centuries and millennia not in quotes or titles should be either spelled out (eighth century) or in Arabic numeral(s) (8th century). The same style should be used throughout any article.
    • Forms such as the 1700s are normally best avoided since it may be unclear whether a 10- or 100-year period is meant (i.e. 1700–1709 or 1700–1799).
    • Remember that the 18th century (1701–1800) and the 1700s (1700–1799) do not span the exact same period.
  • Abbreviations for long periods of time: When the term is frequent, combine the abbreviations yr for "years" and ya for "years ago" with prefixes k for "thousand" (kya, kyr), m for "million" (mya, myr), and b for "billion" (bya, byr). In academic contexts, annum-based units are often used: ka (kiloannum), Ma (megaannum) and Ga (gigaannum). Some authorities, such as the British Museum, simply spell out "years ago". For any abbreviation, show the meaning of the unit parenthetically on first occurrence and again where use is extensive, or might be a standalone topic of interest. For source quotations use brackets, as in "a measured Libby radiocarbon date of 35.1 mya [million years ago] had to be calibrated ..."

Era style

  • The default calendar era is the Western Dionysian era system, a year numbering system also known as the Western Christian era (represented by BC and AD), or the Common Era (represented by BCE and CE).
    • BC and AD are the traditional ways of referring to this era. BCE and CE are common in some scholarly texts and religious writings. Either convention may be appropriate.
      • Do not change the established era style in an article unless there are reasons specific to its content. Seek consensus on the talk page before making the change. Open the discussion under a subhead that uses the word "era". Briefly state why the style is inappropriate for the article in question. A personal or categorical preference for one era style over the other is not justification for making a change.
      • BCE and CE or BC and AD are written in upper case, unspaced, without periods (full stops), and separated from the year number by a space (5 BC, not 5BC). It is advisable to use a non-breaking space.
      • AD may appear before or after a year (AD 106, 106 AD); the other abbreviations appear after (106 CE, 3700 BCE, 3700 BC).
      • Do not use CE or AD unless the date or century would be ambiguous without it (e.g. "The Norman Conquest took place in 1066" not 1066 CE nor AD 1066). On the other hand, "Plotinus was a philosopher living at the end of the 3rd century AD" will avoid unnecessary confusion. Also, in "He did not become king until 55 CE" the era marker makes it clear that "55" does not refer to his age. Alternatively, "He did not become king until the year 55."
      • Use either the BC–AD or the BCE–CE notation consistently within the same article. Exception: do not change direct quotations.
  • Uncalibrated (bce) radiocarbon dates: Some source materials will indicate whether a date is calibrated or not simply by a change in capitalisation; this is often a source of confusion for the unwary reader. Do not give uncalibrated radiocarbon dates (represented by the lower-case bce unit, occasionally bc or b.c. in some sources), except in directly quoted material, and even then include a footnote, a square-bracketed editor's note [like this], or other indication to the reader what the calibrated date is, or at least that the date is uncalibrated. Calibrated and uncalibrated dates can diverge surprisingly widely, and the average reader does not recognise the distinction between bce and BCE / BC.
  • BP: In scientific and academic contexts, BP (before present) is often used. This is calibrated from January 1, 1950, not from the date of publication, though the latter introduces an insignificant error when the date is distant or an approximation (18,000 BP). BP years are given as 18,000 BP or spelled out as 18,000 years before present (not 18,000 YBP, 18,000 before present, 18,000 years before the present, or similar.) Do not convert other notations to BP unless you are certain of what you are doing. A safer and less complex alternative may be to just use "ya (years ago)".
  • Other era systems may be appropriate in an article. In such cases, dates should be followed by a conversion to Dionysian (or vice versa) and the first instance should be linked: "Qasr-al-Khalifa was built in 221 AH (836 CE)" or "in 836 AD (221 AH)".
    • Astronomical year numbering follows the Common Era and does not require conversion, but the first instance of a non-positive year should still be linked: "The March equinox passed into Pisces in year −67."

Julian and Gregorian calendars

Dates can be given in any appropriate calendar, as long as the date in either the Julian or Gregorian calendars is provided, as described below. For example, an article on the early history of Islam may give dates in both Islamic and Julian calendars. Where a calendar other than the Julian or Gregorian is used, this must be clear to readers.

  • Current events are given in the Gregorian calendar.
  • Dates before the adoption of the Gregorian calendar on 15 October 1582 are normally given in the Julian calendar. The Julian day and month should not be converted to the Gregorian calendar, but the start of the Julian year should be assumed to be 1 January (see below for more details).
  • Dates for Roman history before 45 BC are given in the Roman calendar, which was neither Julian nor Gregorian. When (rarely) the Julian equivalent is certain, it may be included.
  • The Julian or Gregorian equivalent of dates in early Egyptian and Mesopotamian history is often debatable. Follow the consensus of reliable sources, or indicate their divergence.
  • Dates of events in countries using the Gregorian calendar are given in the Gregorian calendar. This includes some of the Continent of Europe from 1582, the British Empire from 14 September 1752, and Russia from 14 February 1918 (see the Gregorian calendar article).

The dating method used should follow that used by reliable secondary sources. If the reliable secondary sources disagree, choose the most common used by reliable secondary sources and note the usage in a footnote.

At some places and times, dates other than 1 January were used as the start of the year. The most common English-language convention was the Annunciation Style used in Britain and its colonies until 1752, in which the year started on 25 March, Annunciation Day; see the New Year article for a list of other styles. 1 January is assumed to be the opening date for years; if there is reason to use another start-date, this should be noted.

If there is a need to mention Old Style or New Style dates in an article (as in the Glorious Revolution), a footnote should be provided on the first usage, stating whether the New Style refers to a start of year adjustment or to the Gregorian calendar (it can mean either).

Time zones

When writing a date, first consider where the event happened and use the time zone there. For example, the date of the attack on Pearl Harbor should be December 7, 1941 (Hawaii time/date). If it is difficult to judge where, consider what is significant. For example, if a hacker based in Japan attacked a Pentagon computer in the US, use the time zone for the Pentagon, where the attack had its effect.

If known, include the UTC date and time of the event in the article, indicating that it is UTC; before approximately 1962 indicate UT.[3] For example:

8 p.m. Eastern Standard Time on January 15, 2001 (01:00 UTC, January 16)

Alternatively, just include the UTC offset:

21:00 British Summer Time (UTC+1) on 27 July 2012

While it is a rare situation, the time zone in which some historical events took place has been changed since that epoch. (For example, China under the Republic was divided into five time zones—see Historical time zones of China—while all of modern China is UTC+8.) Be sure to show the UTC or offset appropriate to the clock time then in use, not the modern time zone, wherever they may differ.

Numbers

Numbers as figures or words

As a general rule, in the body of an article, single-digit whole numbers from zero to nine are spelled out in words; numbers greater than nine, if they are expressed in one or two words, may be rendered in numerals or in words (16 or sixteen, 84 or eighty-four, 200 or two hundred); those requiring more than two words are given in numerals (3.75, 544, 21 million). This applies to both ordinal and cardinal numbers. However there are frequent exceptions to these rules.

  • In tables and infoboxes, quantitative data is expressed as numerals; numerals will also fit better in limited space. Numbers within a table's explanatory text and comments should be consistent with the general rule.
  • Comparable quantities should be all spelled out or all figures: we may write either 5 cats and 32 dogs or five cats and thirty-two dogs, not five cats and 32 dogs.
  • Adjacent quantities that are not comparable should usually be in different formats: twelve 90-minute volumes or 12 ninety-minute volumes is more readable than 12 90-minute volumes or twelve ninety-minute volumes.
  • Numbers that begin a sentence are spelled out, since using figures risks the period being read as a decimal point or abbreviation mark; it is often better to recast the sentence than to simply change format, which may produce other problems; e.g. do not use Nineteen forty five and 1950 were important elections for the Labour Party, but rather The elections of 1945 and 1950 were important for the Labour Party.
  • The numerical elements of dates and times are not normally spelled out (that is, do not use the seventh of January or twelve forty-five p.m. or Two thousand eight was the year that ... ). However, they should be spelled out where customary in historical references such as Seventh of March Speech and Fifth of November; these are treated as proper names.
  • Centuries are given in figures or words using adjectival hyphenation where appropriate: the 5th century BCE; nineteenth-century painting. Neither the ordinal nor the word "century" should be capitalised.
  • Common fractions for which the numerator and denominator can be expressed in one word are usually spelled out, e.g. a two-thirds majority; use figures if they occur with an abbreviated unit, e.g. 14 yd and not a quarter of a yd.
  • Mixed fractions are usually expressed in figures, e.g. 2 14; however, the fractional part should always be consistent with the integral part, e.g. Nine and a half, and not Nine and 12.
  • Percentages are usually written with figures, e.g. 10 percent or 10%.
  • Numbers in mathematical formulae are never spelled out (3 < π < 22/7, not three < π < 22 sevenths).
  • Do not use spelled-out numbers before symbols for units of measurement: write five minutes, 5 minutes, or 5 min, but not five min.
  • Measurements, stock prices, and other quasi-continuous quantities are normally stated in figures, even when the value is a small positive integer: 9 mm, The option price fell to 5 within three hours after the announcement.
  • Ages are typically stated in figures, unless it is a large, approximate quantity: an 8-year-old child, the 69-million-year-old fossil.
  • When expressing large approximate quantities, it is preferable to write them spelled out, or partly in figures and part as a spelled‑out named number; e.g. one hundred thousand troops may be preferable to 100,000 troops when the size of the force is not known exactly; write Japan has the world's tenth largest population, with about 128 million people (as it is just an approximation to a number likely to be anywhere between 127,500,000 and 128,500,000), but The movie grossed $28,106,731 on its opening day (the exact quantity).
  • Sometimes, the variety of English used in an article may call for the use of a numbering system other than the Western thousands-based system. For example, the South Asian numbering system is conventionally used in South Asian English. In those situations, link the first spelled-out instance of each quantity (e.g. [[crore]], which yields crore). (If no instances are spelled out, provide a note after the first instance directing the reader to the article about the numbering system.) Also, provide a conversion to Western numbers for the first instance of each quantity, and provide conversions for subsequent instances if they do not overwhelm the content of the article. For example, write three crore (thirty million). Similarly, if you write 3,00,00,000, also write (30,000,000) or (30000000). (Note that the variety of English does not uniquely determine the method of numbering in an article. Other considerations, such as conventions used in mathematics, science and engineering, may also apply, and the choice and order of formats and conversions is a matter of editorial discretion and consensus.)
  • When both a figure and spelled-out named number are used in a quantity, it is useful to use a non-breaking space, as in 128&nbsp;million or 128{{nbsp}}million to prevent a line break from occurring between them.
  • Sometimes figures and words may carry different meanings, for example Every number except one implies that there is one exception (we don't know which), while Every number except 1 means that the specific number 1 is the exception.
  • Proper names, formal numerical designations, and other idioms comply with common usage; e.g. write Chanel No. 5, 4 Main Street, 1-Naphthylamine, Channel 6, Fourth Amendment, Seventeenth Judicial District, Seven Years' War. This is the case even where it causes a numeral to open a sentence, although this is usually avoided by rewording.

Typography

  • Spelled-out two-word numerals from 21 to 99 are hyphenated (e.g. fifty-six), as are fractions (e.g. seven-eighths). Do not hyphenate other multi-word numbers (five hundred, not five-hundred).
  • Where a whole number in a percentage is spelled out, the percent sign is not used (three percent, not three %).
  • The ordinal suffix (st, nd, rd, or th) is not superscripted (123rd and 496th, not 123rd and 496th).
  • The dot (.) or ordinal mark (º) should not be used as an ordinal suffix, except in direct quotations.

Delimiting (grouping of digits)

  • Numbers with five or more digits to the left of the decimal point (i.e. 10,000 or greater) should be delimited into groups so they can be easily parsed, such as by using a comma (,) every three digits (e.g. 12,200, 255,200, 8,274,527). A full stop (.) should not be used to separate thousands (e.g. 12.200, 255.200) to avoid confusion with the decimal point.
  • Numbers with four digits to the left of the decimal point may or may not be delimited (e.g. 1250 or 1,250).
  • Numbers are not delimited when they are part of mailing and shipping addresses, page numbers, or years with four or fewer digits; years with five or more digits should be delimited (e.g. 10,400 BC).
  • In scientific articles, particularly those directed to an expert readership, numbers may be delimited with thin spaces using the {{gaps}} template: {{gaps|8|274|527}} produces 8274527 (note: the thin space character and its HTML entity, &thinsp;, do not render correctly on some browsers or on screen readers used by visually impaired people).
  • Numbers with more than four digits to the right of the decimal point, particularly those in engineering and science where distinctions between different values are important, may be separated (delimited) into groups using the {{val}} template, which uses character-positioning techniques rather than distinct characters to form groups. According to ISO convention (observed by the NIST and the BIPM), it is customary to not leave a single digit at the end, so the last group comprises two, three, or four digits: 1.123, 1.1234, 1.12345, 1.123456, 1.1234567, 1.12345678, 1.123456789, etc. The {{val}} template handles these grouping details automatically; e.g. {{val|1.1234567}} generates 1.1234567 (with a four-digit group at the end), but it can parse no more than a total of 15 significant digits in the significand. For significands longer than this, delimit high-precision values using the {{gaps}} template; e.g. {{gaps|1.234|567|890|123|456}}1.234567890123456.
  • Constants in mathematics-oriented articles may be grouped in fives; e.g. 3.141592653589793238462643383279....
  • The style of delimiting numbers must be consistent throughout an article.

Large numbers

  • Large round numbers are generally assumed to be approximations; only where the approximation could be misleading is it necessary to qualify with words such as about.
  • Avoid excessively precise values where they are unlikely to be stable or accurate, or where the precision is unnecessary in the context. The sentence The speed of light in a vacuum is 299,792,458 metres per second may well be appropriate since it is precisely that value; The distance from the Earth to the Sun is 149,014,769 kilometres and The population of Cape Town is 2,968,790 are not appropriate, because neither value is stable at that level of precision. The template {{undue precision}} can be used to tag such figures.
  • Scientific notation (e.g. 5.8×107 kg) is preferred in scientific contexts; editors can use the {{val}} template, which generates such expressions with the syntax {{val|5.8|e=7|u=kg}}.
  • Where values in the millions occur a number of times through an article, upper-case M may be used for million, unspaced, after spelling out the first occurrence (e.g. She bequeathed her fortune of £100 million unequally: her eldest daughter received £70M, her husband £18M, and her three sons £4M each.).
  • The named numbers billion and trillion are understood to be short scale, 109 and 1012 respectively (see Long and short scales). After the first occurrence in an article, billion may be abbreviated to unspaced bn ($35bn). The prefixes giga-, tera-, and larger and their symbols G, T, ... should be limited to computing and scientific contexts.

Minus sign

Unary minus sign () may constitute a part of numeral. This is the case for negative numbers (−17) and also, for small numbers in the scientific notation, in exponent (10−12). The use of hyphen-minuses (-) instead of proper minus signs has several disadvantages and should be avoided.[4] Keyboard-friendly notations such as -17, 10-12 or mol-1 can suddenly appear wrapped in a browser window, making the quantity unreadable.

The unary minus sign can be produced with the &minus; markup code.

There should be no space between a unary "−" and the numeral, for negative numbers, whereas the sign for the binary operation of subtraction does require a space: xy = 1 and x = −1 are correct, but x = − 1 is incorrect.

Fractions

  • The templates {{frac}} (e.g. N pq) and {{sfrac}} (e.g. N p/q) are available for representing common fractions.
  • Unless there is sound reason to the contrary, fractional parts of metric units should be expressed as decimal fractions (5.25 mm), not vulgar fractions (5 14 mm). However Imperial, English, avoirdupois, and United States customary units may use either form – both (5.25 inches) and (5 14 inches) are acceptable, provided that there is consistency in the way that the fractions are represented.
  • In science and mathematics articles, fractions should always be written either with a horizontal fraction bar (as in \textstyle\frac{1}{2} or 1/2), or with a forward slash and with the baseline of the numbers aligned with the baseline of the surrounding text (as in 1/2). The use of {{frac}} (such as 12) is discouraged in these articles.
  • The use of the few Unicode symbols available for fractions (such as ½) is discouraged entirely, for accessibility reasons among others.
  • Use of the ordinal suffix (e.g. th) with fractions expressed in figures is discouraged (e.g. 1/100, not 1/100th).

Decimal points

  • A decimal point is used between the integer and the fractional parts of a decimal; a comma is never used in this role (6.57, not 6,57).
  • The number of decimal places should be consistent within a list or context (The response rates were 41.0 and 47.4 percent, respectively, not The response rates were 41 and 47.4 percent, respectively), except if the quantities were measured with different precisions.
  • Numbers between −1 and +1 require a leading zero (0.02, not .02); exceptions are sporting performance averages (.430 batting average) and commonly used terms such as .22 caliber.

Percentages

  • Percentages are usually written with figures, e.g. 10 percent or 10%.
  • Percent (American English) or per cent (British English) is commonly used to indicate percentages in the body of an article. The symbol % is more common in scientific or technical articles and in complex listings.
  • The symbol is unspaced (71%, not 71 %).
  • In tables and infoboxes, the symbol % is normally preferred to the spelled-out percent or per cent.
  • Ranges should be formatted with one rather than two percentage signifiers (22–28%, not 22%–28%).
  • Avoid ambiguity in expressing a change of rates. This can be done by using percentage points, not percentages, to express a change in a percentage or the difference between two percentages; for example, The agent raised the commission by five percentage points, from 10 to 15% (if the 10% commission had instead been raised by 5%, the new rate would have been 10.5%). It is often possible to recast the sentence to avoid the ambiguity (raised the commission from 10% to 15%). Percentage point should not be confused with basis point, which is a hundredth of a percentage point.

Repeating decimals

The preferred way to indicate a repeating decimal is to place a bar over the digits that repeat. To achieve this the template {{overline}} can be used. For example, the markup 14.{{overline|285714}} gives 14.285714 and the fraction 3289000 (0.036444…) can be written in decimal form as 0.036{{overline|4}} rendering 0.0364.

Consider a short explanation of this notation (called a vinculum) the first time it is used in an article. Some authors place the repeating digits in parentheses rather than using an overbar (perhaps because overbars are not available in their typesetting environment) but this should be avoided in PhysicsWiki to avoid confusion with expressing uncertainty.

Non-base-10 notations

For numbers expressed in bases other than base ten:

  • In computer-related articles, use the C programming language prefixes 0x (zero-ex) for hexadecimal and 0 (zero) for octal. For binary, use 0b. Consider including a note at the top of the page about these prefixes.
  • In all other articles, use subscript notation. For example: 1379, 2416, 2A912, A87D16 (use <sub> and </sub>).
  • For base eleven and higher, use whatever symbols are conventional for that base. One quite common convention, especially for base 16, is to use upper-case A–F for digits from 10 through 15 (0x5AB3).

Scientific notation, engineering notation, and uncertainty

Notations

  • The template {{val}} can be used to facilitate the generation of scientific notation. It is a flexible tool that allows editors great latitude and must have arguments (each section between the vertical bars) properly entered in order for it to generate output that is compliant with formatting conventions.
  • Scientific notation is done in the format of: one leading digit – decimal marker – remaining digits ×10n, where n is the integer that produces a single leading digit.
    • 1.602×10−19 is a proper use of scientific notation.
    • 160.2×10−17 is not a proper use of scientific notation.
  • Engineering notation is done in the format of: leading digits – decimal marker – remaining digits ×10n, where n is a multiple of 3. The number of leading digits is not more than three.
    • 132.23×106 is a proper use of engineering notation.
    • 1.3223×108 is not a proper use of engineering notation.
  • It is clearer to avoid mixing scientific notation and engineering notation in the same context (do not write A 2.23×102 m2 region covered by 234.0×106 grains of sand).
  • Use discretion when it comes to using scientific and engineering notation. Not all values need to be written in it.
    • Sometimes it is useful to compare values with the same power of 10 (often in tables) and scientific or engineering notation might not be appropriate.
    • Either notation will distinguish the level of precision in a round number such as 5,000, which may mean 5×103 (estimated to the nearest thousand), 5.0×103 (to the nearest hundred), 5.00×103 (to the nearest ten), or 5.000×103 (to the unit).

Uncertainty

  • Where the degree of uncertainty has not been calculated, or is not important to specify, round off to the number of significant digits. If this is not known, be conservative. For instance, an estimate of the number of speakers of a language is unlikely to be accurate beyond two or three digits, even if the source reports seven or eight. Figures suspected of having too many digits can be tagged as {{undue precision}}.
    • Do not use "approximately" with numbers that have simply been rounded off, as this is misleading. For example, a measurement of "40 km" would normally be understood to refer to a distance closer to 40 km than to 30 or 50 km (that is, within 40 ± 5 km), while "approx. 40 km" would suggest a greater uncertainty than this, such as an estimate of 20–60 km.
  • Where the uncertainty has been calculated and is relevant, it can be written in various formats:
    • Value ± uncertainty × 10n unit
      • For example, (1.534±0.35)×1023 m
      • Do not group value and uncertainty in parenthesis before the multiplier: (15.34 ± 0.35) × 1023 m.
    • Value ± percent unit
      • For example, 12.34 ± 5% m2 (not used with scientific notation)
    • Value +uncertainty[superscript] −uncertainty[subscript] × 10n unit
      • For example, 15.34+0.43
        −0.23
        ×1023 m
    • Value(uncertain digits) × 10n unit
      • For example, 1.604(48)×10−4 J means that the calculated value is 1.604×10−4 J and has uncertainty 0.048×10−4 J.
  • The template {{val}} may be used to automatically handle all of this.

Units of measurement

Which units to use

Science-related articles

UK engineering-related articles

  • In UK engineering-related articles, including all bridges and tunnels: generally use the system of units that the topic was drawn-up in, whether metric or imperial. Provide conversions where appropriate.
  • Road distances and speeds are an exception to this: use imperial units with a metric conversion.

Other articles

For other articles, PhysicsWiki has adopted a system of writing a "main" quantity followed by a conversion in parentheses (see Unit conversions below).

  • In non-science US-related articles: the main quantity is generally expressed in US customary units (97 pounds (44 kg)).
  • In non-science and non-engineering UK-related articles: the main quantity is generally expressed in metric units (44 kilograms (97 lb)), but imperial units are still used as the main units in some contexts, including:[5]
    • miles, miles per hour, and fuel consumption in miles per imperial gallon;
    • feet/inches and stones/pounds for personal height and weight;
    • imperial pints for draught beer/cider and bottled milk.
    • hands for horses and most other equines
  • All other articles: the main unit is generally an SI unit or a non-SI unit officially accepted for use with the SI.

How to present quantities

  • Nominal and defined quantities should be given in the original units first, even if this makes the article inconsistent: for example, When the Republic of Ireland adopted the metric system, the road speed limit in built-up areas was changed from 30 miles per hour (48 km/h) to 50 kilometres per hour (31 mph). (The focus is on the change of units, not on the 3.6% increase.)
  • Quantities should be accompanied by a proper citation of the source using a method described at the style guide for citation.
  • In cases where the primary units in the article are different from the primary units in the source:
    • Ensure that the precision of the converted quantity in the article appropriately matches the precision of the quantity from the source.
    • Consider quoting the source quantity in the citation, particularly when the source only provides one system of units.
    • In some cases it may be useful to avoid this by taking the unit used by the source as primary.

SI standard

  • SI units are written according to the SI standard unless otherwise specified in this Manual of Style (dates and numbers). For example see American spelling.
  • Non-SI units in tables 6, 7, 8, and 9 of the SI brochure are written according to the SI standard unless otherwise specified in this Manual of Style (dates and numbers). For example see guidance on litre.
  • Non-SI units mentioned elsewhere in the SI brochure are written according to the SI standard unless otherwise specified in this Manual of Style (dates and numbers). For example see Percentages.

Unit conversions

Where English-speaking countries use different units for the same quantity, follow the "primary" quantity with a conversion in parentheses. This enables more readers to understand the quantity. Examples: the Mississippi River is 2,320 miles (3,734 km) long; the Murray River is 2,375 kilometres (1,476 mi) long.

  • With imperial units which are not also US customary units, double conversions can be useful: The song's second verse reveals that Rosie weighs 19 stone (266 lb; 121 kg).
  • Generally, conversions to and from metric units and US or imperial units should be provided, except:
    • When inserting a conversion would make a common or linked expression awkward (The four-minute mile).
    • When units are part of the subject of a topic—nautical miles in articles about the history of nautical law, SI units in scientific articles, yards in articles about American football—it can be excessive to provide conversions every time a unit occurs. It could be best to note that this topic will use the units (possibly giving the conversion factor to another familiar unit in a parenthetical note or a footnote), and link the first occurrence of each unit but not give a conversion every time it occurs.
  • Converted quantity values should use a level of precision similar to that of the source quantity value, so the Moon is 380,000 kilometres (240,000 mi) from Earth, not (236,121 mi). However, small numbers may need to be converted to a greater level of precision where rounding would cause a significant distortion, so one mile (1.6 km), not one mile (2 km).
  • Category:Conversion templates can be used to convert and format many common units, including {{convert}}, which includes non-breaking spaces.
  • In a direct quotation, always keep the source units.
    • Conversions required for quantities cited within direct quotations should appear within square brackets in the quote.
    • Alternatively, you can annotate an obscure use of units (e.g. five million board feet of lumber) with a footnote that provides conversion in standard modern units, rather than changing the text of the quotation. See the style guide for citation, footnoting and citing sources.

Conversion errors

Conversion errors may occur in general reports, so use the primary sources or the most authoritative sources available. This can help avoid rounding errors, like this: a general report stated that the Eurostar is designed for speeds of "186 mph (299 km/h)". However, the actual design speed was 300 km/h. (The error crept in because the original speed had been converted to 186 mph and then back to km/h.) When common conversion factors are given as quantities, this is a clue that there may be conversion problems. For example, if a number of moons are given estimated diameters in increments of 16 km or 6 miles (implied precision ±0.5 km or mi), it is likely that the estimates in the primary source were in increments of a less-precise 10 miles or 10 km (implied precision ±5 miles or km).

See uncertainty in data above.

Straightforward and accurate conversion may not be possible for loose estimates. For example, if the diameter of a moon is estimated to be 10 miles to within an order of magnitude, any simple conversion to kilometers would introduce a significant loss of accuracy or a gross change in precision. That is because an order-of-magnitude estimate of 10 miles implies a possible range of ≈ 3–30 miles, which would be ≈ 5–50 km. A secondary source will commonly convert such an estimate to a specious 16 km.

Unit names and symbols

Unit names and symbols should follow the practice of reliable sources; the following guidelines may be helpful:

Conventions

  • In prose it is usually better to spell out unit names, but symbols may also be used when a unit (especially one with a very long name) is used many times in an article. However, spell out the first instance of each unit in an article (for example, the typical batch is 250 kilograms ... and then 15 kg of emulsifier is added), except for unit names which are hardly ever spelled out even in publications for general audiences (e.g. the degree Celsius).
  • Where space is limited, such as in tables, infoboxes, and parenthetical notes, and in mathematical formulas, unit symbols are preferable.
  • If a unit symbol which can be unfamiliar to a general audience is used in an article, it should be shown parenthetically after the first use of the full unit name: for example, His initial betatron reached energies of 2.3 megaelectronvolts (MeV), while subsequent betatrons achieved 300 MeV.
  • Numerical ranges use unspaced en dashes if only one unit symbol is used at the end (e.g. 5.9–6.3 kg), and spaced en dashes if two symbols are used (e.g. 3 μm – 1 mm); ranges in prose can be specified using either unit symbol or unit names, and units can be stated either after both numerical values or after the last (e.g. from 5.9 to 6.3 kilograms, from 5.9 kilograms to 6.3 kilograms, from 5.9 to 6.3 kg and from 5.9 kg to 6.3 kg are all acceptable).
  • Dimensions may be given using the multiplication sign or "by".
    • When dimensions are given using the multiplication sign each number should be followed by a unit name, abbreviation or symbol (e.g. write 1 m × 3 m × 6 m, not 1 × 3 × 6 m or 1 × 3 × 6 m3).
    • When dimensions are given using "by" only the last number need be followed by the unit name, abbreviation or symbol (1 by 3 by 6 metres is acceptable).
Unit names
  • Unit names are common nouns. Write them in lower case except where: common nouns take a capital; otherwise specified in the SI brochure; otherwise specified in this manual of style.
  • When unit names are combined by multiplication, separate them with a hyphen or a space (e.g. newton-metre or newton metre). The plural is formed by pluralising the last unit name (e.g. ten newton-metres).
    • When units of torque or energy are formed by multiplication of a unit of force with a unit of length, distinguish these by putting the force unit first for torque (e.g. newton-metres or pound-feet) and the length unit first for energy (e.g. foot-pounds or foot-pounds force).
  • When unit names are combined by division, separate them with per (e.g. meter per second, not meter/second). The plural is formed by pluralising the unit preceding the per (e.g. ten metres per second).
  • When they form a compound adjective, values and unit names should be separated by a hyphen: for example, a five-day holiday.
American spelling

American spellings of unit names should be used on pages written in American English. See "Specific units" section.

Unit symbols
  • Units symbols are preceded by figures, not by spelled-out numbers: for example, 5 km, not five km.
  • Values and unit symbols are separated by a non-breaking space. The {{nowrap}} template or the &nbsp; character can be used for this purpose. For example, use 10 m or 29 kg, not 10m or 29kg.
    • Exceptions: Non-alphabetic symbols for degrees, minutes and seconds for angles and coordinates and the percent sign are unspaced (for example, 5° 24′ 21.12″ N for coordinates, 90° for an angle, 47% for a percentage, but 18 °C for a temperature). See also the "Geographical coordinates" section.
  • Write unit symbols in upright roman type. (Italic type is normally reserved for variables and the like.) (e.g. 10 m or 29 kg, not 10 m or 29 kg).
  • Standard symbols for units are undotted; e.g. m for the metre (not m.), kg for the kilogram (not kg.), in for the inch (not in., the quotation mark ", or the double prime ), and ft for foot (not ft., the apostrophe ', or the prime ).
    • Non-standard abbreviations should be dotted.
  • Symbols are identical in singular and plural—an s is never appended e.g. km, in, lb, not kms, ins, lbs.
  • When unit symbols are combined by multiplication, use a middle dot (&middot;) or a non-breaking space (&nbsp;) to separate the symbols. For example, ms is the symbol for the millisecond, while m·s or m s is the symbol for the metre-second.
  • When unit symbols are combined by division, use a slash to separate the symbols (e.g. for the metre per second use the symbol m/s, not mps) or use negative exponents (m·s−1). Exceptions include mph for the mile per hour, psi for pounds per square inch, etc.
    • Follow a slash in a compound unit symbol with exactly one symbol or parenthesis (e.g. kg/(m·s), not kg/m/s or kg/m·s).
  • Write powers of unit symbols with HTML e.g. 5 km<sup>2</sup> not Unicode superscripts and subscripts. HTML superscripts are easier to read.
  • The abbreviations sq and cu (e.g. 15 sq mi and 3 cu ft) may be used for US customary and imperial units but not for SI units.
  • Unit symbols/abbreviations, apart from those listed below, are written in either non-alphabetic characters or in lower-case letters unless they are derived from a proper name, in which case the first letter is a capital letter.[6] (This applies to the unit itself, not its prefix).
  • Do not use the prefixes M for 103, MM for 106, or B for 109; use SI prefixes instead.

Quantities of bytes and bits

In quantities of bits and bytes, the prefixes kilo (symbol k or K), mega (M), giga (G), tera (T), etc. are ambiguous. They may be based on a decimal system (like the standard SI prefixes), meaning 103, 106, 109, 1012, etc., or they may be based on a binary system, meaning 210, 220, 230, 240, etc. The binary meanings are more commonly used in relation to solid-state memory (such as RAM), while the decimal meanings are more common for data transmission rates, disk storage and in theoretical calculations in modern academic textbooks.

Prefixes for multiples of
bits (b) or bytes (B)
Decimal
Value Metric
1000 k kilo
10002 M mega
10003 G giga
10004 T tera
10005 P peta
10006 E exa
10007 Z zetta
10008 Y yotta
Binary
Value JEDEC IEC
1024 K kilo Ki kibi
10242 M mega Mi mebi
10243 G giga Gi gibi
10244 Ti tebi
10245 Pi pebi
10246 Ei exbi
10247 Zi zebi
10248 Yi yobi

Follow these recommendations when using these prefixes in PhysicsWiki articles:

  • Following the SI standard, a lower-case k should be used for "kilo-" whenever it means 1000 in computing contexts, whereas a capital K should be used instead to indicate the binary prefix for 1024 according to JEDEC. (If, under the exceptions detailed further below, the article otherwise uses IEC prefixes for binary units, use Ki instead).
  • Do not assume that the binary or decimal meaning of prefixes will be obvious to everyone. Explicitly specify the meaning of k and K as well as the primary meaning of M, G, T, etc. in an article ({{BDprefix}} is a convenient helper). Consistency within each article is desirable, but the need for consistency may be balanced with other considerations.
  • The definition most relevant to the article should be chosen as primary for that article, e.g. specify a binary definition in an article on RAM, decimal definition in an article on hard drives, bit rates, and a binary definition for Windows file sizes, despite files usually being stored on hard drives.
  • Where consistency is not possible, specify wherever there is a deviation from the primary definition.
  • Disambiguation should be shown in bytes or bits, with clear indication of whether in binary or decimal base. There is no preference in the way to indicate the number of bytes and bits, but the notation style should be consistent within an article. Acceptable examples include:
    A 64 MB (64 × 10242 byte) video card and a 100 GB (100 × 10003 byte) hard drive
    A 64 MB (64 × 220 byte) video card and a 100 GB (100×109 byte) hard drive
    A 64 MB (67,108,864 byte) video card and a 100 GB (100,000,000,000 byte) hard drive
  • Avoid inconsistent combinations such as A 64 MB (67,108,864 byte) video card and a 100 GB (100 × 10003 byte) hard drive. Footnotes, such as those seen in Power Macintosh 5500, may be used for disambiguation.
  • Unless explicitly stated otherwise, one byte is eight bits (see History of byte).

The IEC prefixes kibi-, mebi-, gibi-, etc. (symbols Ki, Mi, Gi, etc.) are rarely used, even in technical articles (see Complete rewrite of Units of Measurements (June 2008)), so are generally not to be used except under the following circumstances:

  • when the article is on a topic where the majority of cited sources use the IEC prefixes,
  • when directly quoting a source that uses the IEC prefixes,
  • in articles specifically about or explicitly discussing the IEC prefixes,
  • when an article uses both, binary and decimal units intermixed and no primary usage can be determined with certainty, or converting all other occurrences of units into the primary unit would be misleading or lose necessary precision, or declaring the actual meaning of a unit on each occurrence would be impractical.

PhysicsWiki follows common practice regarding bytes and other data traditionally quantified using binary prefixes (e.g. mega- and kilo-, meaning 220 and 210 respectively) and their unit symbols (e.g. MB and KB). Despite the IEC's 1998 guideline creating several new binary prefixes (e.g. mebi-, kibi-) to distinguish the meaning of the decimal SI prefixes (e.g. mega- and kilo-, meaning 106 and 103 respectively) from the binary ones, consensus on PhysicsWiki currently favours the retention of the binary prefixes in computing-related contexts. Use 256 MB of RAM, not 256 MiB of RAM.

Specific units

Name Symbol Comment
arcminute Equal to 1/60 degree (angle). Avoid apostrophe (') as symbol for this purpose.
arcsecond Equal to 1/60 arcminute. Avoid double quote (") as symbol for this purpose.
bit bit Other symbols for bit (such as b or B) should be replaced with bit. This is to reduce confusion with byte. Similarly, bps should be replaced with bit/s.
byte B or byte Other symbols for byte (such as b or o (French: octet)) should be replaced with B or byte. This is to reduce confusion with bit. Similarly, kBps or KBps should be replaced with kB/s or kbyte/s.
gram calorie cal Also known as the small calorie. Lower case 'c' in symbol. SI prefixes can be used e.g. "kilocalorie". Ambiguous unit: in science or technology (e.g. chemistry or nuclear energy) calorie refers to the gram calorie; in food calorie may refer to the kilogram calorie. SI units should always be provided to eliminate ambiguity.
kilogram calorie Cal Also known as the large calorie. Upper case 'C' in symbol. Ambiguous unit: in science or technology (e.g. chemistry or nuclear energy) calorie refers to the gram calorie; in food calorie may refer to the kilogram calorie. SI units should always be provided to eliminate ambiguity. Do not use metric prefixes with the large calorie. The regular rules for common nouns apply to the calorie. Write 100 calories not 100 Calories.
carat carat The metric carat, 200 mg (0.2 g; 0.007055 oz), is used for measurement of gemstones and pearls.
carat or karat k or Kt used as a measurement of purity of gold alloys
cubic centimetre cm3 The non-SI symbol cc may be used to refer to engine volume e.g. Honda motorcycles engines. The form cc must be linked to cubic centimetre on first use in each article.
degree ° (&deg;) Other symbols (e.g. masculine ordinal º or ring) should be replaced. The degree is used for temperature and angle.
degree centigrade °C A synonym for degree Celsius. May be used in quotations and historical contexts, otherwise should be replaced by degree Celsius.
foot ft Similarly 'foot per second' is ft/s rather than fps. Cubic foot is cu ft rather than cf, 'cubic foot per second' is cu ft/s rather than cfs. One million cubic feet is 1 million cubic feet or 1,000,000 cu ft rather than 1 MCF
hand h or hh 4 inches (100 mm), used in measurement of horses in both US and UK English, a radix point followed by additional inches specifies intermediate heights. h is "hands, hh is "hands high," a common dialect variation.
imperial fluid ounce imp fl oz The version (imperial) must be specified. The version (fluid) must be specified to avoid confusion with ounce weight. Same applies to pint and quart.
imperial gallon imp gal The version (imperial) must be specified.
knot kn The symbol 'kt' is reserved for kilotonne. The symbol 'kN' is reserved for kilonewton.
litre

(liter in American English)

l or L The symbol l can look like the digit 1 when without prefix.
long ton long ton This unit must always be spelled out in full.
metre

(meter in American English)

m
micron μm A synonym for micrometre. A link to micrometre is required on first use in each article. The symbol μ may be used in quotations and historical contexts, otherwise it should be replaced by μm.
mile mi Use statute mile rather than mile in nautical and aeronautical contexts to avoid confusion with nautical mile.
mile per hour mph
nautical mile nmi (or NM) The symbol nm is reserved for nanometre. Use nautical mile rather than mile in nautical and aeronautical contexts to avoid confusion with statute mile.
pound per square inch psi
short ton short ton This unit must always be spelled out in full.
tonne

(metric ton in American English)

t Other symbols (such as mt or MT) should be replaced with t.
troy ounce ozt The version (troy) must be specified. Same applies to troy pound. Ambiguity with this unit is so frequent that articles about precious metals, black powder, and gemstones should always specify whether ounces and pounds are avoirdupois or troy.
US fluid ounce US fl oz The version (US) must be specified. The version (fluid) must be specified to avoid confusion with ounce weight. Same applies to pint and quart.
US gallon US gal The version (US) must be specified.
year a Only when SI prefixes are used e.g. "540 Ma old"

Currencies

Which one to use

  • In country-specific articles, such as Economy of Australia, use the currency of the country.
  • In non-country-specific articles such as Wealth, use US dollars ($123), euros (€123), or pounds sterling (£123).

Formatting

  • Use the full abbreviation of a currency on its first appearance (e.g. A$52); subsequent occurrences can use just the symbol of the currency (e.g. $88), unless this would be unclear. The exception to this is in articles related entirely to EU-, UK- or US-related topics, in which the first occurrence may also be shortened (€26, £22 or $34 respectively), unless this would be unclear. When there are different currencies using the same symbol in an article, use the full abbreviation (e.g. US$ for the US dollar and A$ for the Australian dollar, rather than just $), unless the currency which is meant is clear from the context.
  • Do not place a currency symbol after the value (e.g. 123$, 123£, 123€), unless the symbol is normally written as such. Do not write $US123 or $123 (US).
  • Currency abbreviations that come before the number are unspaced if they consist of or end in a symbol (£123, €123), and spaced if alphabetic (R 75).
  • If there is no common English abbreviation or symbol, use the ISO 4217 standard.
  • Format ranges with one, rather than two, currency signifiers ($250–300, not $250–$300).
  • Conversions of less familiar currencies may be provided in terms of more familiar currencies, such as the US dollar, euro or pound sterling using an appropriately chosen rate – this is often not the most recent exchange rate. Conversions should be in parentheses after the original currency, rounding to avoid excess or false precision (one or two significant digits are usually enough, as the exchange rates can vary significantly), with at least the year given as a rough point of conversion rate reference; e.g. Since 2001 the grant has been 10,000,000 Swedish kronor (US$1.4M, €1.0M, or £800k as of August 2009), not (US$1,390,570, €971,673 or £848,646).
  • For obsolete currencies, provide if possible an equivalent, formatted as a conversion, in the modern replacement currency (e.g. decimal pounds for historical pre-decimal pounds-and-shillings figures), or at least a US-dollar equivalent as a default in cases where there is no modern equivalent.
  • When possible, always link the first occurrence of lesser-known currencies (146 Mongolian tögrögs).
  • The names of currencies, currency subdivisions, coins and banknotes should not be capitalised except where normal capitalisation rules require this (for example, at the start of a sentence).
  • When called on to use a plural with the euro, use the standard English plurals and not the "legislative" plurals (ten euros and fifty cents, not ten euro and fifty cent). In adjectival use, no plural form is generally used, but rather a hyphenated form: (a two-euro pen, a ten-dollar meal, a ten-cent coin).
  • The pound sterling is represented by the £ symbol, with one horizontal bar. The double-barred symbol is ambiguous, as it has also been used for the Italian lira and other currencies. For non-British currencies that use pounds or a pound symbol (e.g. the Irish pound, IR£) use the symbol conventionally preferred for that currency.

Common mathematical symbols

See also: Manual of Style (mathematics).
  • For a negative sign or subtraction operator, use a minus sign (). You can input a minus sign by either keying in &minus; or by clicking on it in the insert box beneath the edit window (located between the ± and × signs). Do not use an en dash (), do not use a hyphen (-) unless writing code, and do not use an em dash ().
  • For a multiplication sign, use ×, which can be input by clicking on it in the edit toolbox under the edit window or by keying in &times; (however, the letter x is accepted as a substitute for by in such terms as 4x4).
Common mathematical symbols
Name Operation Other use Symbol CER NCR Unicode As binary operator
(e.g. 1 + 1)
As unary operator
(e.g. +1)
Plus sign Addition Positive sign + &plus; &#43; U+002B Spaced Unspaced
Minus sign Subtraction Negative sign &minus; &#8722; U+2212 Spaced Unspaced
Plus or minus Addition or subtraction Positive or negative sign ± &plusmn; &#177; U+00B1 Spaced Unspaced
Minus or plus Subtraction or addition Negative or positive sign &#8723; U+2213 Spaced Unspaced
Multiplication sign, cross Multiplication, vector product × &times; &#215; U+00D7 Spaced
Division sign, obelus Division ÷ &divide; &#247; U+00F7 Spaced
Equal sign Equation = &#61; U+003D Spaced
Not equal sign Non-equation &ne; &#8800; U+2260 Spaced
Approximate sign Approximation &asymp; &#8776; U+2248 Spaced
Less than sign Inequation < &lt; &#60; U+3C Spaced
Less than or equal to Inequation &le; &#8804; U+2264 Spaced
Greater than sign Inequation > &gt; &#62; U+3E Spaced
Greater than or equal to Inequation &ge; &#8805; U+2265 Spaced

Geographical coordinates

For draft guidance on, and examples of, coordinates for linear features, see PhysicsWiki:WikiProject Geographical coordinates/Linear.
Quick guide:
Quick how to
To add Lua error: callParserFunction: function "#coordinates" was not found. to the top of an article, use {{Coord}}, thus:
{{Coord|57|18|22|N|4|27|32|W|display=title}}

These coordinates are in degrees, minutes, and seconds of arc.

'title' means that the coordinates will be displayed next to the title.

To add Lua error: callParserFunction: function "#coordinates" was not found. to the top of an article, use either
{{Coord|44.112|N|87.913|W|display=title}}

or

{{Coord|44.112|-87.913|display=title}}

These coordinates are in decimal degrees.

  • Degrees, minutes and seconds must be separated by a pipe ("|").
  • Map datum must be WGS84 (except for off-earth bodies).
  • Avoid excessive precision (0.0001° is <11 m, 1″ is <31 m).
  • Latitude (N/S) must appear before longitude (E/W).
Optional coordinate parameters follow the longitude and are separated by an underscore ("_"):

Other optional parameters are separated by a pipe ("|"):

  • display
    |display=inline (the default) to display in the body of the article only,
    |display=title to display at the top of the article only, or
    |display=inline,title to display in both places.
  • name
    name=X to label the place on maps (default is PAGENAME)

Thus: {{Coord|44.117|-87.913|dim:30_region:US-WI_type:event

|display=inline,title|name=accident site}}

Use |display=title (or |display=inline,title) once per article, for the subject of the article, where appropriate.

Geographical coordinates on Earth should be entered using a template to standardise the format and to provide a link to maps of the coordinates. As long as the templates are adhered to, a robot performs the functions automatically.

First, obtain the coordinates. Avoid excessive precision.

Two types of template are available:

  • {{coord}} offers users a choice of display format through user styles, emits a Geo microformat, and is recognised (in the title position) by the "nearby" feature of PhysicsWiki's mobile apps and by external partners such as Google (-Maps and -Earth) and Yahoo.
  • Infoboxes such as {{Infobox settlement}}, which automatically emit {{Coord}}.

Depending on the form of the coordinates, the following formats are available.

For just degrees (including decimal values):

{{coord|dd|N/S|dd|E/W}}

For degrees/minutes:

{{coord|dd|mm|N/S|dd|mm|E/W}}

For degrees/minutes/seconds:

{{coord|dd|mm|ss|N/S|dd|mm|ss|E/W}}

where:

  • dd, mm, ss are the degrees, minutes and seconds, respectively;
  • N/S is either N for northern or S for southern latitudes;
  • E/W is either E for eastern or W for western longitudes;
  • negative values may be used in lieu of S and W to depict southern and western hemispheres

For example:

The city of Oslo, located at 59° 55′ N, 10° 44′ E, enter:

{{coord|59|55|N|10|44|E}}—which becomes Lua error: callParserFunction: function "#coordinates" was not found.

For a country, like Botswana, less precision is appropriate:

{{coord|22|S|24|E}}—which becomes Lua error: callParserFunction: function "#coordinates" was not found.

Higher levels of precision are obtained by using seconds:

{{coord|33|56|24|N|118|24|00|W}}—which becomes Lua error: callParserFunction: function "#coordinates" was not found.

Coordinates can be entered as decimal values

{{coord|33.94|S|118.40|W}}—which becomes Lua error: callParserFunction: function "#coordinates" was not found.

Increasing or decreasing the number of decimal places controls the precision. Trailing zeros should be used as needed to ensure that both values have the same level of precision.

London Heathrow Airport, Amsterdam, Jan Mayen and Mount Baker are examples of articles that contain geographical coordinates.

Generally, the larger the object being mapped, the less precise the coordinates should be. For example, if just giving the location of a city, precision greater than 100 meters is not needed unless specifying a particular point in the city, for example the central administrative building. Specific buildings or other objects of similar size would justify precisions down to 10 meters or even one meter in some cases (1′′ ~15 m to 30 m, 0.0001° ~5.6 m to 10 m).

The final field, following the E/W, is available for specification of attributes, such as type, region and scale.

When adding coordinates, please remove the {{coord missing}} tag from the article, if present.

For more information, see the geographical coordinates WikiProject.

Templates other than {{coord}} should use the following variable names for coordinates: lat_d, lat_m, lat_s, lat_NS, long_d, long_m, long_s, long_EW.

See also

Notes

  1. PhysicsWiki:Requests for arbitration/Jguk#Principles, PhysicsWiki:Requests for arbitration/jguk 2#Principles, and PhysicsWiki:Requests for arbitration/Sortan#Principles
  2. This change was made on August 24, 2008, on the basis of this archived discussion. It was ratified in two December 2008 RfCs PhysicsWiki:Manual of Style/Dates and numbers/Three proposals for change to MOSNUM and PhysicsWiki:Manual of Style/Dates and numbers/Date Linking RFC
  3. Dennis D. McCarthy, "Evolution of Timescales from Astronomy to Physical Metrology," Metrologica 48 (2011): S139. This work explains the increasing international use of UTC in the 1960s.
  4. Substitutes for the minus sign as en dash () and non-breaking hyphen () are incorrect not only because these characters are different (and thus hinder automatic processing), but also because of slight differences in vertical positions—the minus sign should have the same alignment as the plus sign (+). Also, in most fonts, dashes are thinner. Dashes were seldom inserted in place of minus signs due to mistakes or misunderstanding the fact that the minus sign has a distinct code point. So, if one sees a symbol which looks like a minus sign in the place of a minus sign in PhysicsWiki, then one may not be sure that it is encoded correctly.
  5. Some editors hold strong views for or against metrication in the UK. If there is disagreement about the main units used in a UK-related article, discuss the matter on the article talk-page, at MOSNUM talk, or both. If consensus cannot be reached, refer to historically stable versions of the article and retain the units used in these as the main units. Note the style guides of British publications such as Times Online (under "Metric").
  6. This definition is consistent with all units of measure mentioned in the 8th edition of the SI brochure and with all units of measure catalogued in EU directive 80/181/EEC