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Since the text "km/h" on this Irish speed limit sign is a symbol, not an abbreviation, it represents both "kilometres per hour" (English) and "ciliméadar san uair"(Irish)[1]

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Background

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Writers often use shorthand to denote units of measure. Such shorthand can be an abbreviation, such as "in" for "inch" or can be a symbol such as "km" for "kilometre". Symbol are sometimes taken from outside the normal character set in use such as "℥", the symbol for the Apothecaries pound.

The shorthand "in" applies to English only – in Afrikaans for example, the shorthand "dm" is used for the equivalent Afrikaans word "duim".[2] Since both "in" and "dm" are contractions of the same word, but in different languages, they are abbreviations. A symbol on the other hand, defined as "Mark or character taken as the conventional sign of some object or idea or process"[3] applies the appropriate shorthand by substitution rather than by contraction. Since the shorthand for kilometre (Quilômetro in Portuguese or Χιλιόμετρο in Greek) is "km" in both languages and the letter "k" does not appear in the expansion of either translation, "km" is a symbol as it is a substitution rather than a contraction.

Abbreviation development

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The use of abbreviations[Note 1] for units of measure emerged once the units themselves were sufficiently widely used that readers understood the abbreviations.

Unless recommendations of a central authority exist and are followed, a single entity can have many different, but equivalent abbeviations. For example, the unit of length, the kilometre first made its appearance in English in 1810[4] and the compound unit of speed "kilometeres per hour" was in use by 1866.[5] "Kilometres per hour" did not begin to be abbreviated in print until many years later, with several different abbreviations existing near-contemporaneously.

  • 1889: "k. p. h."[6]
  • 1895: "km:h"[7]
  • 1898: "km/h"[8]
  • 1899: "km./hr." [9]
  • 1915: "km.-hr."[12]
  • 1916: "km. per hour"[13]
  • 1933: "KPH"[14]

With no central authority to dictate the rules for abbreviations, various publishing houses had their own rules that dictated whether upper case letters, lower case letters, periods and so on shoudl be used, reflecting both changes in fashion and the image of the publishing house concerned.[15][16]

Development of symbols in metrology

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The use of symbols to replace words dates back to at least the late Mediaval era when Johannes Widman, writing in German in 1486, used the symbols "+" and "-" to represent "addition" and "subtraction".[17] In the early 1800s Berzelius introduced a symbolic notation for the chemical elements derived from the elements' Latin names.[18] Typically, "Na" was used for the element sodium (Latin: natrium) and H2O for water.

In 1879, four years after the signing of the Treaty of the Metre, the CIPM proposed a range of symbols for the various metric units then under the auspices of the CGPM. Among these were the use of the symbol "km" for "kilometre", "g" from "gram" and so on.[19]

Prior to 1921, the CGPM were guardians of the international prototype kilogram and metre, the IAU were guardians of time-keeping (which was done using astronomical methods) while the IEC were gaurdians of electrical units of measure. In 1921 the mandate of the CGPM was extended to include all physical units and and over the next few years, the CIPM, on behalf of the CGPM, set about aligning the definitions of the various units of measure and, in conjunction with the IAU, the IEC and other international bodies, made recommendations that ensured a consistent use of units of measure across all physical disciplines. This included the way in which units of measure were written.

In 1948, as part of its the preparatory work for the SI, the CGPM adopted symbols for many units of measure that did not have universally-agreed symbols, one of which was the symbol "h" for "hours". At the same time the CGPM formalised the rules for combining units - quotients could be written in one of three formats resulting in "km/h", "km h-1" and "km•h-1" being valid representations of "kilometres per hour".[20] The SI standards, which were MKS-based rather than CGS-based were published in 1960 and have since then have been adopted by many authorities around the globe including academic publishers and legal authorities.

The SI explicitly states that unit symbols are not abbreviations and are to be written using a very specific set of rules.[20] M. Danloux-Dumesnils[21] provides the following justification for this distinction:

It has already been stated that, according to Maxwell, when we write down the result of a measurement, the numerical value multiplies the unit. Hence the name of the unit can be replaced by a kind of algebraic symbol, which is shorter and easier to use in formulae. This symbol is not merely an abbreviation but a symbol which, like chemical symbols, must be used in a precise and prescribed manner.

Measurement shorthand – symbol or abbreviation

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Road sign in China – "km" is a symbol, not an abbreviation, as it is not a contraction of a Chinese word

In the International System of Units (SI) manual[22] the word "symbol" is used consistently to define the shorthand used to represent the various SI units of measure. The manual also defines the way in which units should be written, the principal rules being:

  • The conventions for upper and lower case letters must be observed – for example 1 MW (megawatts) is equal to 1,000,000,000 mW (milliwatts).
  • No periods should be inserted between letters – for example "m.s" (which is an approximation of "m·s", which correctly uses middle dot) is the symbol for "metres multiplied by seconds", but "ms" is the symbol for milliseconds.
  • No periods should follow the symbol unless the syntax of the sentence demands otherwise (for example a full stop at the end of a sentence).
  • The singular and plural versions of the symbol are identical – not all languages use the letter "s" to denote a plural.

Writing unit symbols and the values of quantities

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  • The value of a quantity is written as a number followed by a space (representing a multiplication sign) and a unit symbol; e.g., "2.21 kg", "7.3×102 m2", "22 K". This rule explicitly includes the percent sign (%). Exceptions are the symbols for plane angular degrees, minutes and seconds (°, ′ and ″), which are placed immediately after the number with no intervening space.[23][24]
  • Symbols for derived units formed by multiplication are joined with a centre dot (·) or a non-break space; e.g., N·m or N m.
  • Symbols for derived units formed by division are joined with a solidus (/), or given as a negative exponent. E.g., the "metre per second" can be written m/s, m s−1, m·s−1, or . Only one solidus should be used; e.g., kg/(m·s2) and kg·m−1·s−2 are acceptable, but kg/m/s2 is ambiguous and unacceptable.
  • Symbols are mathematical entities, not abbreviations, and do not have an appended period/full stop (.).
  • Symbols are written in upright (Roman) type (m for metres, s for seconds), so as to differentiate from the italic type used for quantities (m for mass, s for displacement). By consensus of international standards bodies, this rule is applied independent of the font used for surrounding text.[25]
  • Symbols for units are written in lower case (e.g., "m", "s", "mol"), except for symbols derived from the name of a person. For example, the unit of pressure is named after Blaise Pascal, so its symbol is written "Pa", whereas the unit itself is written "pascal".[26]
    • The one exception is the litre, whose original symbol "l" is unsuitably similar to the numeral "1" or the uppercase letter "i" (depending on the typeface used), at least in many English-speaking countries. The American National Institute of Standards and Technology recommends that "L" be used instead, a usage common in the US, Canada, and Australia (but not elsewhere). This has been accepted as an alternative by the CGPM since 1979. The cursive ℓ is occasionally seen, especially in Japan and Greece, but this is not currently recommended by any standards body. For more information, see litre. The litre is not an SI unit per se and is expressed in SI terms as a cubic decimetre, i.e., dm3.
  • A prefix is part of the unit, and its symbol is prepended to the unit symbol without a separator (e.g., "k" in "km", "M" in "MPa", "G" in "GHz"). Compound prefixes are not allowed.
  • All symbols of prefixes larger than 103 (kilo) are uppercase.[27]
  • Symbols of units are not pluralised; e.g., "25 kg", not "25 kgs".[25]
  • The 10th resolution of CGPM in 2003 declared that "the symbol for the decimal marker shall be either the point on the line or the comma on the line." In practice, the decimal point is used in English-speaking countries and most of Asia, and the comma in most of Latin America and in continental European languages.[28]
  • Spaces may be used as a thousands separator (1000000) in contrast to commas or periods (1,000,000 or 1.000.000) in order to reduce confusion resulting from the variation between these forms in different countries. In print, the space used for this purpose is typically narrower than that between words (commonly a thin space).
  • Any line-break inside a number, inside a compound unit, or between number and unit should be avoided, but, if necessary, the last-named option should be used.
  • In Chinese, Japanese, and Korean language computing (CJK), some of the commonly used units, prefix-unit combinations, or unit-exponent combinations have been allocated predefined single characters taking up a full square. Unicode includes these in its CJK Compatibility and Letterlike Symbols subranges for back compatibility, without necessarily recommending future usage. These are summarised in Unicode symbols.
  • When writing dimensionless quantities, the terms 'ppb' (parts per billion) and 'ppt' (parts per trillion) are recognised as language-dependent terms, since the value of billion and trillion can vary from language to language. SI, therefore, recommends avoiding these terms.[23] However, no alternative is suggested by the International Bureau of Weights and Measures (BIPM).

Writing the unit names

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  • Names of units follow the grammatical rules associated with common nouns: in English and in French they start with a lowercase letter (e.g., newton, hertz, pascal), even when the symbol for the unit begins with a capital letter. This also applies to 'degrees Celsius', since 'degree' is the unit. In German however, names of units, in common with all nouns, start with a capital letter.[29]
  • Names of units are pluralised using the normal English grammar rules,[30][31]

e.g. "henries" is the plural of "henry".[30]: 31  The units lux, hertz, and siemens are exceptions from this rule: they remain the same in singular and plural form. Note that this rule applies only to the full names of units, not to their symbols.

  • When unit names are combined by multiplication, they are separated with a hyphen or a space (e.g. newton-metre or newton metre). The plural is formed by pluralising the last unit name as above (e.g. ten newton-metres).
  • The official US spellings for deca, metre, and litre are deka, meter, and liter, respectively.[32]

Current non-standard representations

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Several representations of "kilometres per hour" have been used since the term was introduced and many are still in use today. For example, dictionaries list "km/h", "kmph" and "km/hr" as English abbreviations and the SI representations are 'km/h', 'km h-1' and 'km•h-1' and are classified as symbols.

for example style guides of news organisations such as Reuters[33] and The Guardian[16] tend to use "kph" for "kilometres per hour" and "C" or "F" instead of "°C" or "°F" for temperature.

Notes

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  1. ^ The Oxford Concise Dictionary defines "abreviate" as "Make short (chiefly now of writing part of a word for whole ...)

References

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  1. ^ Traffic Signs Manual (PDF). Department of Transport / An Roinn Iompair. November 2010. Page 1/13. Retrieved 16 July 2012. {{cite book}}: Italic or bold markup not allowed in: |publisher= (help)
  2. ^ Abel Coetzee, ed. (1969). Woordeboek/Dictionary; Afrikaans-English / Engels-Afrikaans. Glasgow and Johannesburg: Collins. OCLC 29232187.
  3. ^ Oxford Concise Dictionary. Oxford University Press. 1964.
  4. ^ "The Oxford English Dictionary". Retrieved July 13, 2012.
  5. ^ Frazer, John F. (1866). Journal of the Franklin Institute of the State of Pennsylvania for the Promotion of the Mechanic Arts. Vol. LII. Philedelphia: Franklin Institute. p. 314. {{cite book}}: Unknown parameter |Number= ignored (|number= suggested) (help)
  6. ^ Harrington, Mark W., Rotch, A. Lawrence and Herdman, W. J. (1889). American meteorological journal: A monthly review of meteorology, medical climatology and geography. Meteorological Journal Company. p. 226. {{cite book}}: Unknown parameter |Volume= ignored (|volume= suggested) (help)CS1 maint: multiple names: authors list (link)
  7. ^ Pell-r, G. (?) (1895). "Power consumed on electric railways". The Street Railway Journal. 11 (2): 116–117. {{cite journal}}: Unknown parameter |month= ignored (help)
  8. ^ Bulletin - United States Geological Survey, Volumes 151-152. USGS. 1898. pp. ix.
  9. ^ Whipple, F. J. W. (1899). "The Stability of the Motion of a Bicycle". The Quarterly Journal of Pure and Applied Mathematics. 30: 342.
  10. ^ Ball, Jack (1911). "Foreign Notes on Aviation". Town & Country: 26. {{cite journal}}: Unknown parameter |month= ignored (help)
  11. ^ Dodd, S. T. (1914). "A Review of Some European Electric Locomotive Designs". General Electric Review. 17 (1): 1141. {{cite journal}}: Unknown parameter |month= ignored (help)
  12. ^ a b "Data on Mixed Motor Fuels of Interest for American Export Trade". The Automobile. 33 (15): 709. 1915. {{cite journal}}: Unknown parameter |month= ignored (help)
  13. ^ "Tractive resistance tests with an electric motor truck". Engineering and Contracting. 46 (25): 560. 1916. {{cite journal}}: Unknown parameter |month= ignored (help)
  14. ^ Aircraft Year Book. Aerospace Industries Association of America, Manufacturers Aircraft Association, Aeronautical Chamber of Commerce of America. 1933. pp. 391–393. {{cite book}}: Unknown parameter |Volume= ignored (|volume= suggested) (help)
  15. ^ Truss, Lynne (2003). Eats Shoots and Leaves. Profile Books. pp. 188–189. ISBN 1 86197 6127.
  16. ^ a b Marsh, David (2007). Guardian Style. The Guardian. ISBN 978 0 85265 086 8.
  17. ^ O'Connor, John J.; Robertson, Edmund F., "Johannes Widman", MacTutor History of Mathematics Archive, University of St Andrews
  18. ^ The History of Chemical Symbols (PDF), Greenville, South Carolina: BJU Press, retrieved 18 July 2012
  19. ^ Quinn, Terry (2012). From Artefacts to Atoms: The BIPM and the Search for Ultimate Measurement Standards. Oxford: Oxford University Press. p. 132. ISBN 978-0-19-530786-3.
  20. ^ a b International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 124, ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16
  21. ^ Danloux-Dumesnils (1969). The Metric System: A Critical Study of its Principles and Practice. The Athlone Press of the University of London. p. 32.
  22. ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16
  23. ^ a b The International System of Units (SI) (PDF) (8 ed.). International Bureau of Weights and Measures (BIPM). 2006. pp. 134–135.
  24. ^ Thompson, A.; Taylor, B. N. (July 2008). "NIST Guide to SI Units — Rules and Style Conventions". National Institute of Standards and Technology. Retrieved 2009-12-29.
  25. ^ a b "Chapter 5. Writing unit symbols and names, and expressing the values of quantities". The International System of Units (SI) (PDF) (8 ed.). International Bureau of Weights and Measures (BIPM). 2006.
  26. ^ Ambler Thompson and Barry N. Taylor, (2008), Guide for the Use of the International System of Units (SI), (Special publication 811), Gaithersburg, MD: National Institute of Standards and Technology, section 6.1.2
  27. ^ Ambler Thompson and Barry N. Taylor, (2008), Guide for the Use of the International System of Units (SI), (Special publication 811), Gaithersburg, MD: National Institute of Standards and Technology, section 4.3.
  28. ^ Williamson, Amelia A (March – April 2008). "Period or Comma? Decimal Styles over Time and Place" (PDF). Science Editor. 31 (No 2). Council of Science Editors: 42. Retrieved 2012-05-19. {{cite journal}}: |number= has extra text (help); Check date values in: |date= (help)
  29. ^ Wörterbuch Englisch Dictionary German. Limassol: Eurobuch/Eurobooks. 1988.
  30. ^ a b Ambler Thompson & Barry N. Taylor (2008). "NIST Special Publication 811: Guide for the Use of the International System of Units (SI)" (PDF). National Institute of Standards and Technology. Retrieved 2008-06-18. {{cite journal}}: Cite journal requires |journal= (help)
  31. ^ "Interpretation of the International System of Units (the Metric System of Measurement) for the United States" (PDF). Federal Register. 73 (96). National Archives and Records Administration: 28432–3. 9 May 2008. FR Doc number E8-11058. Retrieved 2009-10-28.
  32. ^ "The International System of Units" (PDF). pp. iii. Retrieved 2008-05-27.
  33. ^ Reuters Handbook of Journalism (PDF). Reuters. April 2008. p. 278.
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