The Defining Constants of the International System of Units

November 1, 2017|Posted in: Uncategorized

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Defining Constant	Symbol	Numerical Value	Unit
hyperfine transition frequency of Cs	∆vcs	9 192 631 770	Hz
speed of light in a vacuum	c	299 792 458	m/s
Planck constant*	h	6.62607015 x 10-34	J/Hz
elementary charge*	e	1.602176634 x 10-19	C
Boltzman constant*	k	1.380649 x 10-23	J/K
Avogadro constant*	NA	6.0220140 76 x 1023	/mol
luminous efficacy	Kcd	683	lm/W

*These numbers are from the CODATA 2017 special adjustment.  They were calculated from the data available before the 1^st July 2017.