1. An apparatus for measuring the effective resolution of a digitizer of the type which samples an input signal at a sampling frequency f.sub.s and produces a sequence of digital data representing sampled magnitudes of said input signal, the apparatus comprising: means for generating a sinewave signal, said sinewave signal being applied as said input signal to said digitizer such that said digitizer produces an N-element distal data sequence representing measured magnitudes of said sinewave signal; and means responsive to said digital data sequence for determining therefrom estimated amplitude, frequency, phase angle and offset parameters characterizing said sinewave signal, for computing in accordance with said estimated parameters a set of data values representing estimated magnitudes of said sinewave signal, and for determining the effective resolution of said digitizer in accordance with a combination of differences between said measured magnitudes and said estimated magnitudes of said sinewave signal.