American National Standard Letter Symbols for Units of Measurement (SI Units@ Customary Inch-Pound Units@ and Certain Other Units) (Revision and Redesignation of IEEE Std 260-1978)
"This standard covers letter symbols(Footnote 1) for units of measurement. It does not include abbreviations for technical terms@ nor does it cover symbols for physical quantities.(Footnote 2) The symbols given in this standard are intended for all applications@ including use in text and equations; in graphs and diagrams; and on panels@ labels@ and nameplates. Footnote 1 - ""Letter symbol"" as a technical term does not have the same meaning as either ""name"" or ""abbreviation."" An abbreviation is a letter or a combination of letters (plus sometimes an apostrophe or a full stop@ i.e.@ a period) that by convention represents a word or a name in a particular language; hence@ an abbreviation may be different in a different language. A symbol represents a physical quantity or a unit and is therefore independent of language. For example@ the symbol for electromotive force is E@ whereas the abbreviation is emf in English@ fem in French@ and EMK in German. The unit names ""ampere"" and ""second"" have sometimes been abbreviated amp and sec@ respectively@ but this usage is now deprecated. The standard unit symbols for ampere and second are A and s@ respectively. Footnote 2 - As used in this standard@ the term physical quantity means a measurable attribute of phenomena or matter. Examples are length@ mass@ and time."