A dwell meter is simply a voltmeter with a different scale. "Dwell", the time the points are closed ("dwell together") will read as zero volts at the terminal on the downstream side of the coil since the points are connected to ground. When the points are open, the meter will read full battery voltage, since no current is flowing. For instance- - - -30 degrees of dwell (out of a possible 45 degrees) which is normal for a V8 engine means the meter is grounded 66% of the time. The 66%/33% relationship of zero volts/battery volts will yield a cranking measurement of approximately 4 volts if the battery voltage is 12. While running, with an alternator voltage of 14 will give a "dwell" voltage of around 4.6 volts at the (-) coil terminal. A 66% dwell setting for a 6 cylinder engine of 40 degrees will yield a similar voltage reading. Since a digital meter will respond too quickly to the voltage changes, an analog meter works best for setting dwell as a function of voltage. A digital meter will usually yield an unintelligible random display.
Jerry
