Dictionary · Standards & Units
International System of Units (SI)
The system of units based on the ISQ, with unit names, symbols, prefixes, and rules for their use, adopted by the CGPM. Since the 2019 revision all seven base units are defined by fixing the numerical values of seven defining constants.
Related terms
More from Standards & Units
Reference data
Data related to a property of a phenomenon, body, or substance — or to a system of components of known composition or structure — obtained from an identified source, critically evaluated, and verified for accuracy.
VIM (JCGM 200:2012) 5.16
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
Standard reference data
Reference data issued by a recognized authority — the CODATA constants and NIST standard reference databases are the working examples.
VIM (JCGM 200:2012) 5.17
Quantity equation
A mathematical relation between quantities in a system of quantities, independent of units — v = l/t regardless of whether metres or inches are used.
VIM (JCGM 200:2012) 1.22
International measurement standard
A standard recognized by signatories to an international agreement and intended to serve worldwide.
VIM (JCGM 200:2012) 5.2
Reference quantity value
A quantity value used as a basis for comparison with values of quantities of the same kind — a true value, a conventional value, or a standard's certified value, depending on context.
VIM (JCGM 200:2012) 5.18