!!! Overview
[{$pagename}], have been Since [2019|Year 2019], the magnitudes of all [SI Base Units] have been defined by declaring that seven constants that have certain exact [numerical|Number] values when expressed in terms of their [SI Base Units] or [SI Derived Unit].
||Symbol||Name||Exact value
|Δ''ν''%%sub Cs/%|[hyperfine transition frequency of Cs|https://en.wikipedia.org/wiki/Caesium_standard]|9,192,631,770 [Hz]
|[c]|[speed of light|https://en.wikipedia.org/wiki/Speed_of_light]|299,792,458 m/s
|[h]|[Planck constant|https://en.wikipedia.org/wiki/Planck_constant]|6.62607015×10%%sup −34/% [J]⋅[s]
|[e]|[elementary charge|https://en.wikipedia.org/wiki/Elementary_charge]|1.602176634×10%%sup −19/% C
|[k]|[Boltzmann constant|https://en.wikipedia.org/wiki/Boltzmann_constant]|1.380649×10%%sup −23/% [J]/[K]
|[N]%%sub A/%|[Avogadro constant|https://en.wikipedia.org/wiki/Avogadro_constant]|6.02214076×10%%sup 23/% [mol]%%sup −1/%
|[K]%%sub cd/%|[luminous efficacy|https://en.wikipedia.org/wiki/Luminous_efficacy] of 540 THz radiation|683 lm/W!! More Information
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