The SI system of units have been revamped recently.

Instead of being based on 7 base units, it is now based on 7 physical constants. Don’t worry. The magnitude of the 7 base units (kg, m , s, etc) are not affected. It’s only the way they are defined that have been changed.

The seven defining constants are:

the caesium hyperfine frequency Δν_{Cs}

the speed of light in vacuum c

the Planck constant h

the elementary charge e

the Boltzmann constant k

the Avogadro constant N_{A}, and

the luminous efficacy of a defined visible radiation K_{cd}

Watch the following video if you’re interested to know the rational for the change.