User:Martinvl/Sandbox/km per h

Notation History
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.

Abbreviation development
The use of abbreviations dates back to antiquity, but abbreviations for "kilometres per hour" did not appear in the English language until the late nineteenth century.

Although the unit of length kilometer first made its appearance in English in 1810, the compound unit of speed "kilometers per hour" was first observed no later than 1866. "Kilometers per hour" did not begin to be abbreviated in print until many years later, with several different abbreviations existing near-contemporaneously.

With no central authority to dictate the rules for abreviations, various publishing houses have their own rules that dictate whether to use upper case letters, lower case letters, periods and so on, reflecting both changes in fashion and the image of the publishing house concerned, for example style guides of news organisations such as Reuters and The Guardian tend to use "kph" (along with "C" or "F" instead of "°C" or "°F" for temperature).

Kilometers per hour as a symbol


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". In the early 1800's Berzelius introduced a symbolic notation for the chemical elements derived from the elements' Latin names. 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".

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 univerally-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". 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. M. Danloux-Dumesnils 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."

SI, and hence the use of "km/h" (or "km h-1" or "km•h-1") has now been adopted around the world in many areas related to health and safety and in legal metrology. It is also the preferred system of measure in academia and in education

Regulatory use
In 1972 the EU published a directive (overhauled in 1979 to take British and Irish interests into account) that required member states to abandon CGS-based units in favour of SI. The use of SI implicitly required that member states use "km/h" as the shorthand for "kilometres per hour" on official documents.

Another EU directive, published in 1975, regulates the layout of speedometers within the European Union, uses the text "km/h" in all languages. Examples of text that does not include all three letters "k", "m" and "h" in the native language of the state concerned, but where the EU directives applies include:
 * Dutch: "kilometer per uur" ("hour" is spelt "uur" - no "h"),
 * Portuguese: "quilómetro por hora" ("kilometre" is spelt "quilómetro" - no "k")
 * Greek: "χιλιόμετρα ανά ώρα" (a different script).

In 1988 the United States National Highway Traffic Safety Administration promulgated a rule stating that "MPH and/or km/h" were to be used in speedometer displays. On May 15, 2000 this was clarified to read "MPH, or MPH and km/h". However, the Federal Motor Vehicle Safety Standard number 101 ("Controls and Displays") allows "any combination of upper- and lowercase letters" to represent the units.

Current use
In addition to regulatory use (as described above), the notation "km/h" is used in education and but style guides of news organisations such as Reuters and The Guardian tend to use "kph" (along with "C" or "F" instead of "°C" or "°F" for temperature).

Aide memoire from here onwards
The Oxford English Dictionary

The concept of symbols as opposed to abbreviations was introduced during the ninteenth century.
 * History of the standardization effort (including "not an abbrev.")
 * Use in government regulation Europe US ?
 * Use in science
 * Use in industry
 * Style guides (that emphasize uses as a symbol)

The EU directive 80/181/EEC, which requires consistent use and representation of units of measure in all member states for "economic, public health, public safety or administrative purposes"[ref] implicitly catalogues "km/h" as the symbol for "kilometres per hour".


 * Historic development based on User:Garamond Lethe's earlier proposal will be added here

Many academic journals require the use of SI units which implicitly requires the use of "km/h", not "kph", but the style guides for many newspapers mandate the use of "kph" for "kilometres per hour" (along with "C" or "F" rather than °C or °F when writing temperature). '''The EU .... for "kilometres per hour".'''