c is used in the definition of the meter, but you don’t remotely need to know that in day-to-day life. As long as the seven base units (length, time, mass, temperature, electric current, luminosity) end up with reasonable values the system is practically coherent.
(are the values reasonable? well, human-scale capacitors and resistors seem pretty heavily skewed away from the center of the scale…)
(are the values reasonable? well, human-scale capacitors and resistors seem pretty heavily skewed away from the center of the scale…)