An Introdction to the New SI

On November 16, at the 26th General Conference on Weights and Measures in Versailles (Paris, France), a historic decision was taken on the new definitions of the four basic units: kilogram, ampere, kelvin and mole. Now all units will be determined by the fundamental constants of nature - an atom and a quantum. The kilogram is now determined by Planck’s constant, the ampere will be defined as e elementary charges per second, the kelvin will be a change in thermal energy of k joules, and the mole will be the amount of substance that contains N_A elementary entities.