Review on AGPtek® Professional Digital Tachometer Contact by Marc Alvarez

The instructions don't mention that you really have to aim exactly perpendicular to the surface (aim at the center of rotation) to get a reading. It seems like you have to be within 10cm of the target first to get a stable reading, then you can step back a little further, but the 20cm quoted seems a bit exaggerated. However, when used as described, it gives stable and fairly accurate readings (my 3600 rpm grinder read 3585 rpm within 0.4%). Pretty good for the price. I don't know of anyone else.