Relative (rel.)

Abbreviation Rel.
Definition by words Quotient of two identical kinds-of-quantity and components, commonly two kinds-of-quantity related to different systems, the second may be a reference system
Definition by equation
Scope “Relative” is a modifier (adjective) to a kind-of-quantity.

10-6, 10-3, 1 (one), 103, 106, etc.

The unit “1” (one) is ommited in the NPU syntax.

Specification “System 2” needs to be specified in the NPU syntax
Reference Ferard G, Dybkaer R, Fuentes-Arderiu X. Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences : Recommendations 2016. 1 ed: Royal Society of Chemistry; 2016. 182 p. doi:10.1039/9781782622451.