and what about a old time mechanical tach? with the cable its still measuring the RPM'S of the crankshaft
I know the electric tach comes off the dist but its measuring the crankshaft revolutions or showing the cranks RPM's
the crank turns 2:1 of the cam, so the cam is turning 1/2 the speed of the crank there for the tach must double time to produce a accurate RPM reading
SR66