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.

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