Système international d’unités
The SI Units are the most commonly used units for measuring physical sizes.
https://www.bipm.org/en/measurement-units/prefixes.html https://www.bipm.org/en/measurement-units/
The seven defining constants of the SI are:
- the caesium hyperfine frequency DeltanuCs;
- the speed of light in vacuum c;
- the Planck constant h;
- the elementary charge e;
- the Boltzmann constant k;
- the Avogadro constant NA; and
- the luminous efficacy of a defined visible radiation Kcd.