As prepared and announced for a long time, the International System of Units (SI) has undergone a major change of paradigm in defining its units, which enter into force on 20th May 2019.
From 20 May 2019 the International System of Units (SI) has undergone one of the most significant changes since its establishment. The definitions of four units (the kilogram, the ampere, the kelvin and the mole) are now linked to fixed values of four funamental physical constants. These are the Planck constant h, the electron's charge e, the Boltzmann constant kB, and the Avogadro constant NA.
By fixing these values of these constants in the SI system, a definition of the units is realized independent of the paractical realization ensuring ensuring stability and universality of the SI definitions.
You may have a look at our news dated Dec.1st 2018, for a deeper insight, and links to further reading.
News proposed by Hans Werner Schumacher, Physikalisch-Technische Bundesanstalt, from the Editorial Committee of EMA.