Signal power ($P=T^{-1}{\int }_0^T|f(t){|}^{2}dt$)

For a periodic signal, the mean squared magnitude over a period. Its units are the square of the signal's units: a voltage signal has mean-square power in ${\mathrm{V}}^2$. Physical electrical power in a resistive load additionally divides this quantity by electrical resistance. Subtracting the squared mean gives the variance of the signal over a uniformly sampled phase; the two quantities coincide for a zero-mean signal.