As a national metrology institute (NMI), INRIM is responsible for realising, maintaining and developing the reference standards of the measurement units of the International System (SI).
The mere existence of such reference standards guarantees the traceability of every measurement to the SI, meaning the reliability of the measurements and their comparability at international level.
The SI is a language shared by all the countries parties to the Metre Convention, a treaty signed in Paris in 1875.
From 1971, it includes 7 base quantities and their corresponding 7 base units of measurement:
|base quantities||base units|
|amount of substance||mole|
All further units (such as hertz, newton, pascal, watt...) are called derived units since they are then obtained by combining the base units according to the algebraic relations linking the corresponding quantities.
The SI is constantly evolving: over the time, the International System has changed many times! We need only think of its beginnings: the base units were only three: kilogramme. metre, and second. Kelvin, ampere, candela, and mole were added afterwards.
The next approaching change will be the redefinition of the measurement units in terms of fundamental physical constants.
For several years, the metrological community has been working to prepare for this change. It will be a major breakthrough since it will enable more accurate and stable reference standards for the maesurement units. Also, it will be possible to realise such reference standards everywhere.
The 26th meeting of the General Conference on Weights and Measures, to be held on November 13-16, 2018, in Versailles, is expected to ratify this redefinition that will then come into force on May 20, 2019.