The rpm, dwell and timing of an internal combustion engine are measured by starting and stopping a digital counter on the leading edge of pulse waveforms generated either within the engine or by a timing light. To measure rpm and dwell only the low coil signal is used. For rpm measurement, the counter is started when the ignition points open, and stopped upon the next opening of the points. To measure dwell the counter is started by the opening of the points and stopped when the points close, the resultant count being the inverse of dwell, and this count is subtracted from the rpm count to obtain dwell. Timing is measured by starting the counter upon the firing of the number one cylinder, and providing an additional signal delayed in time as a function of the distributor advance to stop the counter. The count in the counter is converted to rpm, dwell or timing by either analog or digital techniques. A high energy ignition adapter circuit prevents triggering of the counter by a false indication of the opening of the points due to a waveform peculiar to low coil signals produced in vehicles using high energy ignition systems. A timing light delay circuit having a variable delay is incorporated with the timing light to produce the delayed signal proportional to distributor advance, the delay being adjustable within two selectable ranges. By measuring and displaying the computed dwell for each cylinder in sequence, distributor mechanical wear associated with shaft bearings and drive gears may be detected. Power contribution and dynamic relative compression for each cylinder may be measured by using the counter to measure the time that the points are open, and the time that the points are closed, for each cylinder in sequence, and displaying the measurements.