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I had to check the manual for my late 60’s Sears Automotive Analyzer. The dwell and tachometer functions are not voltage sensitive for this unit.
Those measurements are really continuity readings. The dwell is reading how long the points are closed compared to being always closed. The tach is measuring how many times per minute the points open and close.
Unfortunately what applies to my meter might not be applicable for more modern solid state or chip driven instruments. You need to check the specs and manual for each meter.
