Dictionary · Standards & Units
Base unit
A measurement unit adopted by convention for a base quantity — in the SI: second, metre, kilogram, ampere, kelvin, mole, candela.
Related terms
More from Standards & Units
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
System of units
A set of base and derived units, with their multiples and submultiples, defined under given rules for a given system of quantities.
VIM (JCGM 200:2012) 1.13
Primary measurement standard
A standard established using a primary reference measurement procedure, or created as an artifact chosen by convention — not calibrated against another standard for the same quantity.
VIM (JCGM 200:2012) 5.4
Certified reference material (CRM)
A reference material accompanied by documentation issued by an authoritative body providing property values with uncertainties and traceability using valid procedures — per ISO 17034 practice.
VIM (JCGM 200:2012) 5.14
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
Numerical value equation
A relation between numerical values that holds only for stated units — the form most spreadsheet formulas quietly are, and the reason unit discipline matters.
VIM (JCGM 200:2012) 1.25