I used the tiny tach to do rpm tune ups, set idle, etc. Could easily run into the cabin to watch while driving, and it's installation is just wrapping around a spark plug wire and grounding the other wire...after that, it's one wire into the cabin. Good investment to see exactly what rpm you're at.
Also, you could just connect an average dwell meter, most have rpm settings, if you wanted to just see temporarily what rpm each, say, 5 mph above 50 is.
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