An analog voltmeter can also be used as a dwell meter. It will read the average of the "points open" and "points closed" voltage. With the engine running and clean points with little or no resistance, points closed voltage at the downstream (distributor) side of the coil will be virtually zero since the points are grounded. Points open voltage will be the same as battery terminal voltage, since there's no current flow. A 66% dwell reading (30 degrees on a V8 with a 45 degree cam lobe separation) will be 1/3 of battery voltage, since the points are closed 2/3 of the time. A 40 degree dwell setting on a 6 lobe distributor cam will show the same 1/3 of battery voltage reading. Simple math!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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