How it works: First, mark the edge of the machine whose rotational speed you want to find. Ensure that the machine is placed in suitable darkness. Now, go to the app, turn it on, and in the input field, enter the approximate value of RPM. Focus your flashlight on the rotating machine, then adjust the RPM using the bar up or down until the mark on the machine appears stationary. Read the value from the input field; this is the RPM of your rotating machine. Features of the RPM Meter - Strobe Li