Saw referenced this on another site:
Single Channel Digital Ignition Tester
Part No. 8998
-Hand held tester generates a trigger signal to check the operation of MSD single channel Ignitions and the coil (6, 7, 8 and 10 Series Ignition Controls)
-LCD display shows the simulated RPM and can be used to confirm the operation of rev limits, rpm activated switches, shift lights and tachometers
-Additional circuit will check the operation of cam sync signals
-Triggers through breaker points, amplifier and magnetic pickup trigger inputs from the MSD Ignition
-Can be used on 4, 6 and 8-cylinder engines