The sensor has 2 bolts securing it but out of the engine anything metallic sets off massive fluctuations in readings anything from 2,000 to 160,000. I have adremel with an rpm display, I mounted a magnet on it andthe sensor reads, butbeing about 1,000rpmout.
If the magnet is moved about then the readingsfluctuate.

I have ordered a simple sensor to make my own see if that helps..

Antony