Abstract: Apparatus and method for extracting the fundamental component of a complex waveshape (E.sub.T) and for determining the magnitude (V) and phase .theta. of the fundamental component are disclosed. The complex waveshape is converted into digital data relative to a reference signal (E.sub.R) and the in-phase (x.sub.1) and quadrature (y.sub.1) components of the fundamental component are determined by a graphical Fourier analysis of the digital data so that the magnitude and phase of the fundmental component relative to the reference signal (E.sub.R) can be determined.