[Rich Biebel]

A Tach can easily be tested in the car. Use an MSD tester that allows you to fire the ignition without the engine running. I’ve had tachs that I knew were off and the MSD tester confirmed it. One was off 200 rpm at lower rpms and 400 or more at higher rpms. That was not the first one I’ve had that was off. The tester can test anything rpm related and the ignition itself. I keep it in my trailer toolbox....I don’t recall the part number. Easy to find though. I also have a grid controller in my car and it records all runs for time and rpm ....another good item but not as good as a data recorder ...