I am using this:
http://interface.khm.de/index.php/lab/experiments/frequency-measurement-library/
Are we talking about the same library? Is the above library in the link able to detect zero RPM and speed?
This is the hall effect sensor we use: http://www.digital-speedos.co.uk/hall-effect-speed-sensor-for-drift-gauges-non-magnetic-382-p.asp