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SI base units

Draft Commission Directive amending, for the purpose of its adaptation to technical progress, the Annex to Council Directive 80/181/EEC as regards the definitions of SI base units (3 pages + Annex 3 pages, in English)

This draft Directive intends to update the definitions of the SI base units of Directive 80/181/EEC on units of measurement so as to align them to the ones adopted by the General Conference on Weights and Measures (CGPM) at its 26th meeting in November 2018.

More particularly, the CGPM decided at its 24th meeting in 2011 a new way of defining the SI based on a set of seven defining constants drawn from the fundamental constants of physics and other constants of nature. This decision was confirmed at the 25th meeting of the CGPM in 2014.

At its 26th meeting, the CGPM adopted a resolution adapting, as from 20 May 2019, the definitions of the SI base units of measurement, namely the metre, the kilogram, the second, the ampere, the kelvin, the mole and the candela, corresponding to the seven base quantities of length, mass, time, electric current, thermodynamic temperature, amount of substance and luminous intensity. The new definitions are based on the new principle of fixed numerical values of the defining constants. They are expected to improve the long-term stability and reliability of the SI base units as well as accuracy and clarity of measurements. The draft Directive intends therefore to align the definitions of the SI base units of Directive 80/181/EEC to the new definitions adopted by the CGPM, ensuring thus the uniform implementation of the SI.