At a precise moment during one trial, the resonator might be both in its expanded and its contracted state; a single measurement forces it to "choose" which state to be in.

Moments later, you'll see your heart rate, Systole and Diastole — based on either a single measurement or the average of three measurements in a row.

Using the mean of several measurements to quantify performance is certainly more accurate than using a single measurement, but it can be insufficient for determining which task executes faster.