Abstract: An apparatus and method for analyzing a pair of analog, generally sinusoidal, quadrature gauge signals from a conventional plunger-type gauge head includes digital ratio-metric comparison of signals using floating high and low reference conversion values for analog-to-digital conversion, such values being selectively obtained from the gauge signals and their complements. Intra-quadrant distance values are optionally scaled for detected variations in actual quadrant distance values from assumed nominal values therefor. The intra-quadrant distance value is summed with whole and partial signal cycle distance values to determine a total distance value for a given plunger movement.