By Barry N. Taylor
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Additional resources for The International System of Units (SI)
Sample text
The SI prefixes are used with several of these units, but not with the units of time. Table 6. Non-SI units accepted for use with the International System of Units Quantity Name of unit Symbol for unit Value in SI units time minute hour (a) day degree (b, c) minute second (d) hectare (e) liter (f) metric ton (g) min h d 1 min = 60 s 1 h = 60 min = 3600 s 1 d = 24 h = 86 400 s 1o = (π/180) rad 1′ = (1/60)o = (π/ 10 800) rad 1″ = (1/60)′ = (π/ 648 000) rad 1 ha = 1 hm2 = 104 m2 1 L = 1 dm3 = 103 cm3 = 10−3 m3 1 t = 103 kg plane angle area volume mass o ′ ″ ha L t (a) The symbol for this unit is included in Resolution 7 of the 9th CGPM (1948; CR, 70).
Unit name symbol Although the values of quantities are normally expressed using symbols for numbers and symbols for units, if for some reason the unit name is more appropriate than the unit symbol, the unit name should be spelled out in full. 6 meters per second When the name of a unit is combined with the name of a multiple or sub-multiple prefix, no space or hyphen is used between the prefix name and the unit name. The combination of prefix name plus unit name is a single word. 1. milligram, but not milli-gram In both English and in French, however, when the name of a derived unit is formed from the names of individual units by multiplication, then either a space or a hyphen is used to separate the names of the individual units.
A multiple or sub-multiple prefix, if used, is part of the unit and precedes the unit symbol without a separator. A prefix is never used in isolation, and compound prefixes are never used. Unit symbols are mathematical entities and not abbreviations. Therefore, they are not followed by a period except at the end of a sentence, and one must neither use the plural nor mix unit symbols and unit names within one expression, since names are not mathematical entities. In forming products and quotients of unit symbols the normal rules of algebraic multiplication or division apply.
