I have used my Mac Tools digital light on many motors without too much of a problem. It is a bit finicky, sometimes not triggering and sometimes not locking on 2 Stroke. Most often I can get it to work. It provides a good RPM read when working. Tried to get it to work on this Mercury and I can get the lamp to fire but the RPM shows quite erratically and way high. Bought a new Craftsman, same thing. Is it something about this Mercury that I can't see.