time interval measurements which can more readily be compared one against another in order to accomplish this the data modification procedure matches two mathematical curves to selected peaks and selected valleys respectively of the time interval measurement curve illustrated in fig2 and then uses these matched curves to modify the data more specifically the data modification procedure selects three peaks t2 n2 t3 n3 and t4 n4 which are one engine cycle apart so that each peak represents the peak of an undulation produced by the same cylinder a generalized hyperbolic function f1 having three unknown coefficients is then matched to these three data points so as to provide a mathematical function which varies smoothly and monotonically that is either continually increasing or continually decreasing and which generally follows the peaks of the undulations in the acquired data thereafter two data points corresponding to valleys one engine cycle apart are selected and are used to match a second less generalized hyperbolic function f 2 having only two unknown coefficients the resulting mathematical function will again be smoothly and monotonically varied and will generally follow the valleys of the data the resulting curves f1 and f2 match the acceleration trends of the engine it will be noted that these curves might deviate substantially.