Revision of the International System of Units
On 16 Nov 2018, the final day of the 26th meeting of the General Conference on Weights and Measures (CGPM) at the Palais des Congres in Versailles, a landmark decision was taken and the BIPM Member States voted for the adoption of a Resolution that redefines four of the seven base units of the SI. The definitions of 4 units -the kilogram, the ampere, the kelvin and the mole- have been revised.
The definitions of all the units of the revised SI are now linked to physical constants, which guarantee their stability and universality. The kilogram, the last unit to be defined from an artefact (the famous international prototype of the kilogram, sanctioned by the first CGPM in 1889 and kept at the Pavillon de Breteuil), is now linked to the Planck constant.
Dr Martin J T Milton, Director of BIPM, stated: "The new definitions will use 'the rules of nature to create the rules of measurement' linking measurements at the atomic and quantum scales to those at the macroscopic level. As science and technology progress, the demands for measurements to underpin new products and services will increase. Metrology is a dynamic branch of science and the steps taken by the BIPM and the wider metrology community to advance the SI in 2018 will underpin these requirements ensuring that scientists can study it and engineers can improve it. And, since science and engineering play an important role in our lives, measurement matters for everyone."
IUPAC contributed to the work by coordinating the redefinition of the mole, published earlier in Jan 2018.