Editing Physical quantity (section)

== Components ==
Following [[ISO 80000-1]],<ref name="ISO 80000-1">{{cite web |title=ISO 80000-1:2009(en) Quantities and units — Part 1: General |website=International Organization for Standardization | url=https://www.iso.org/obp/ui/#iso:std:iso:80000:-1:ed-1:v1:en | access-date=2023-05-12}}</ref> any value or [[Magnitude (mathematics)|magnitude]] of a physical quantity is expressed as a comparison to a unit of that quantity. The ''value'' of a physical quantity ''Z'' is expressed as the product of a ''numerical value'' {''Z''} (a pure number) and a unit [''Z'']:

:<math>Z = \{Z\} \times [Z]</math>

For example, let <math>Z</math> be "2 metres"; then, <math>\{Z\} = 2</math> is the numerical value and <math>[Z] = \mathrm{metre}</math> is the unit.
Conversely, the numerical value expressed in an arbitrary unit can be obtained as:

:<math>\{Z\} = Z / [Z]</math>

The multiplication sign is usually left out, just as it is left out between variables in the scientific notation of formulas. The convention used to express quantities is referred to as ''[[quantity calculus]]''. In formulas, the unit [''Z''] can be treated as if it were a specific magnitude of a kind of physical [[dimension]]: see ''[[Dimensional analysis]]'' for more on this treatment.