I know that a tachometer shows rpm, but I would like to calculate the rpm of a rotary shaft, and I'm not sure how to do it. What is the hardware that actually gathers the rpm data?
The Tektronix DC503 frequency counter had an internal slide switch that you could set to provide a display in RPM vs. Hz. Never did see any other counter that did that. I though it could be a really handy feature but never did use it myself.
function generator in pulse mode, and an LED (high brightness white ones work best). frequency in Hz*60=rpm. as was mentioned above, a black mark or a sticker makes for a good "indicator" to use with the strobed LED