Mole: The unit of chemical amount

The need to redefine the kilogram and ampere has been discussed for several decades now. There were many technical reasons to do so [1]. Following the success of the 1983 definition of the meter based on the speed of light in vacuum, the International Committee on Weights and Measures decided that this was also an opportune time to recast the definitions of all seven SI base units in terms of the most stable things known to scientists - physical constants [2].