For more information visit: https://www.nobelprize.org/prizes/physics/1918/planck/biographical/

Redefining the International System of Units (SI) in 2018

In the "New SI" four of the SI base units – namely the kilogram, the ampere, the kelvin and the mole – will be redefined in terms of constants; the new definitions will be based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k_{B}), and the Avogadro constant (N_{A}), respectively. Further, the definitions of all seven base units of the SI will also be uniformly expressed using the explicit-constant formulation, and specific mises en pratique will be drawn up to explain the realization of the definitions of each of the base units in a practical way.

**Key to SI Definition Constants:**Δν = the unperturbed ground state hyperfine transition frequency of the caesium-133 atom ΔνCs is 9,192,631,770 hertz

c = the speed of light in vacuum c is exactly 299,792,458 metres per second

h = the Planck constant h is exactly 6.626 06X x 10

e = the elementary charge e is exactly 1.602 17X x 10

k

N

K

Note: X represents the yet unknown final digit(s).

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