Editing Physical quantity (section)

== Symbols and nomenclature ==

International recommendations for the use of symbols for quantities are set out in [[ISO/IEC 80000]], the [[IUPAP red book]] and the [[Quantities, Units and Symbols in Physical Chemistry|IUPAC green book]]. For example, the recommended symbol for the physical quantity "mass" is ''m'', and the recommended symbol for the quantity "electric charge" is ''Q''.

=== Typography ===
{{further|Mathematical notation}}

Physical quantities are normally typeset in italics.
Purely numerical quantities, even those denoted by letters, are usually printed in roman (upright) type, though sometimes in italics. Symbols for elementary functions (circular trigonometric, hyperbolic, logarithmic etc.), changes in a quantity like Δ in Δ''y'' or operators like d in d''x'', are also recommended to be printed in roman type.

Examples:
* Real numbers, such as 1 or {{radic|2}},
* e, the base of [[natural logarithms]],
* i, the [[imaginary numbers|imaginary]] unit,
* π for the ratio of a circle's circumference to its diameter, 3.14159265...
* δ''x'', Δ''y'', d''z'', representing differences (finite or otherwise) in the quantities ''x'', ''y'' and ''z''
* sin ''&alpha;'', sinh ''&gamma;'', log ''x''