It is well known that the speed [image omitted] is obtained in the process of defining SI units via action-at-a-distance forces, like the force between two static charges and the force between two long and parallel currents. The speed c[subscript u] is then physically different from the observed speed of propagation c associated with electromagnetic waves in vacuum. However, repeated experiments have led to the numerical equality c[subscript u] = c, which we have called the c equivalence principle. In this paper we point out that [image omitted] is the correct form of writing Faraday's law when the c equivalence principle is not assumed. We also discuss the covariant form of Maxwell's equations without assuming the c equivalence principle. (Contains 3 footnotes.)