The cross power spectrum is not typically used as a direct measurement but is an important building block for other measurements.
Use the following equation to compute the two-sided cross power spectrum of two time-domain signals A and B.
The cross power spectrum is a two-sided complex form, having real and imaginary parts. You can convert the cross power spectrum to magnitude and phase in the same way you compute the amplitude and phase spectrums of a power spectrum.
You also can convert the cross power spectrum to a single-sided form. The single-sided cross power spectrum yields the product of the rms amplitudes and the phase difference between the two signals A and B. The units of the single-sided cross power spectrum are in quantity rms squared, for example, Vrms2.
The power spectrum is equivalent to the cross power spectrum when signals A and B are the same signal. Therefore, the power spectrum is often referred to as the auto power spectrum or the auto spectrum.