Strobe light source can be used to measure rotation speed of various machinery parts (e.g. shafts, pulleys, spindles etc.). When the frequency of strobe light equals to the rotation frequency of the measured part human eye (actually brain) perceives the image of the rotating part as stationary (not rotating) - lets call this phenomenon as "perceived stop". Please note that perceived stop occurs at any strobe frequency which is a multiple of actual rotation speed. So for example pulley with 600 RPM will appear non rotating at 10Hz (600 RPM) strobe light, 20Hz (1200 RPM), 30Hz(1800 RPM) and so on. Therefore you should carefully increase strobe frequency to find the lowest Hz which gives perceived stop.

System requirements:
1. Android 6.0 or higher ( application will not work on earlier versions).
2. Phone with camera and integrated flashlight.

Usage:
1. Turn strobe ON by pressing the corresponding button.
2. Point flashing light towards rotating part which RPM you want to measure.
3. Move the slider slowly from left to right and watch for perceived rotation stop of the observed part.
4. Then using increment and decrement buttons tune strobe frequency precisely to obtain good perceived stop of the rotation. Observed part must have several periodic elements e.g. 3 jaws in a chuck or several bolts on a flange. Those periodic elements will produce observed rotation stop effect.
    "RPM" - shows the RPM value corresponding to the current strobe frequency .
    "Hz" - shows current strobe frequency. This is actually measured frequency of the strobe light (measured from the start of one flash to the start of next flash) which includes all delays of code execution.
    "Error (%)" - this is the measure of possible error of strobe frequency. Actual frequency is somewhere between (Hz minus Error) and (Hz plus Error) with 68% probability (i.e. Error is one standard deviation of Hz). This is statistical measure because each strobe cycle has random duration due to the fact that Android is not real time operating system.
    "Smooth readings" - turns On and Off averaging of Hz and RPM. When turned On it allows to see more stable values with less jitter.
    "Flash duration" - allows to control time when flash is on in each strobe cycle. It is recommended to use fastest settings. This will give more "focused" image of perceived stop. On some phones "Fastest" setting doesn't work - the flash doesn't turn on in each cycle or doesn't deliver enough brightness. In this case please use "+2 ms" or "+5 ms" settings.