The tooth-to-tooth time interval of teeth on a flywheel of a rotating internal combustion engine is recorded for at least a significant portion of an engine revolution, the variation in the time intervals are utilized to determine minima in the tooth-to-tooth time intervals, thereby to separate the tooth-to-tooth time intervals to cylinder-by-cylinder groupings. The number of teeth from one minima to the next for a given number of cylinders is summed. The summation of the number of teeth may then be used as a measured count of the number of teeth on the flywheel of the engine; this measured count may be compared against industry standards if desired. In a second embodiment, the measured count is averaged on a per-cylinder basis, and the tooth count for each cylinder is compared therewith and any data more than 20% off the average is eliminated from final computation of an average number of teeth for a given number of cylinders. The invention provides alternative use of engine cycle identification signals or engine tooth waveform analysis to measure the number of teeth on the flywheel.
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