Dictionary · Standards & Units
System of quantities
A set of quantities together with the non-contradictory equations relating them — the framework a system of units is built on.
Related terms
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Ordinal quantity-value scale
A quantity-value scale for ordinal quantities, established by agreement on a procedure — comparisons of order are valid, arithmetic on the values is not.
VIM (JCGM 200:2012) 1.28
Kind of quantity
The aspect common to mutually comparable quantities — length, mass, and energy are kinds; diameter and wavelength are both quantities of the kind length.
VIM (JCGM 200:2012) 1.2
Unit equation
A mathematical relation between base and derived units — N = kg·m·s⁻².
VIM (JCGM 200:2012) 1.23
Coherent derived unit
A derived unit that is a product of powers of base units with no numerical factor other than one — the newton is coherent in the SI; the kilometre per hour is not.
VIM (JCGM 200:2012) 1.12
Intrinsic measurement standard
A standard based on an inherent and reproducible property of a phenomenon or substance — the triple point of water cell, the Josephson voltage standard.
VIM (JCGM 200:2012) 5.10
Conversion factor between units
The ratio of two units for quantities of the same kind — 25.4 mm/in; the numerical value changes, the quantity does not.
VIM (JCGM 200:2012) 1.24