What is the significance of the readings from a handheld tachometer?
Well, a Tachometer in general tells you the RPM of a motor or
other such engine. As for something handheld, from what I have seen
they would mostly be employeed to engines that are not mounted into
a car already as a means of testing their capacity or after some
series of tests that can better determine condition or wear or
such. Most cars have them mounted into their dashboards to my
understanding, to give a reading while on the go.