Please capitalize where necessary: a strobe tachometer is a useful tool because you can't always get access to the machine shaft to stick a piece of reflective tape to use a laser tachometer or make contact with the moving shaft to use a contact tachometer - using a stroboscope you can "stop" the shaft down to 30 rpm (fpm).
A strobe tachometer is a useful tool because you can't always get access to the machine shaft to stick a piece of reflective tape to use a laser tachometer or make contact with the moving shaft to use a contact tachometer - using a stroboscope you can "stop" the shaft down to 30 RPM (FPM).