Abstract: In accordance with the present invention, a measurement instrument employing an improved method for measuring relative compression is provided. The compression signal is first acquired by digitizing the battery voltage over multiple engine cycles using an analog to digital converter (ADC) to obtain a series of digital samples. The compression signal is filtered using a low pass digital filtering technique such as a finite impulse response (FIR) filter along with spike removal that removes high frequency noise and impulse-type ignition noise from the compression signal. The filtered compression signal is then "zero-lined", meaning that each of the peaks corresponding to a compression curve of a cylinder, which are bounded on either side, are re-scaled such that the local minima reside along a zero base line. Next, the zero-lined compression signal is averaged over the multiple cycles of the engine.