It's OK though, because the metre and second are already based on physical constants: the second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and the metre is defined from the second by fixing the speed of light at 299 792 458 m/s.
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It's OK though, because the metre and second are already based on physical constants: the second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and the metre is defined from the second by fixing the speed of light at 299 792 458 m/s.