!!! 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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