SI stands for the International System of Units: the second, metre, kilogram, ampere, kelvin, mole and candela, plus the derived units built from them. Each base unit is defined by fixing the numerical value of a constant of nature, such as the Planck constant for the kilogram and the elementary charge for the ampere. Metrological traceability ultimately means relating a result to realizations of these units.
Customer wants traceability to the SI, not to some vendor's in-house standard, so it has to go through an accredited chain.
Also heard as
- International System of Units
Related terms
Traceability
Proof that a result ties back to the SI or another stated reference, with every calibration in between on record.
NMI
National metrology institute, the body that realizes a country's measurement units at the top of its traceability chain.
Primary standard
A standard that gets its value straight from the unit definition, not from calibration against another standard.
Traceability chain
The documented sequence of calibrations linking a working instrument back to national or SI-level standards.