The service National Standards (Metrology) of the FPS Economy informed us of the following (abstract from BIPM):

In a landmark decision, the BIPM's Member States voted on 16 November 2018 to revise the International System of Units (SI), changing the world's definition of the kilogram, the ampere, the kelvin and the mole.

The decision, made at the 26th meeting of the General Conference on Weights and Measures (CGPM) in Versailles, France, means that all SI units will now be defined in terms of constants that describe the natural world. This will assure the future stability of the SI and open the opportunity for the use of new technologies, including quantum technologies, to implement the definitions.

In the revised SI four of the SI base units – namely the kilogram, the ampere, the kelvin and the mole – are redefined in terms of constants; the new definitions are based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. Further, the new definitions of all seven base units of the SI are also uniformly expressed using the explicit-constant formulation, and specific mises en pratique will be drawn up to explain the realization of the definitions of each of the base units in a practical way.

The new definitions will come into force on 20 May 2019.

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