I'm a retired calibration & controls guy.
I have a client with a testing machine that uses a 60 tooth wheel for rpm.
The sensor (magnetic? hall effect? prox?) was lost. Of course, no records.
The sensor's output was sent to an f/v converter - Analog Decives, Inc. 5B45-05.
Spec. pdf is at...
The frequency of the inspections should determine your investment in the measuring process. If this must be checked several times per hour, then a very expensive equipment is justified - even automation of measurements.
If only 1x/month or so, then your contract inspection is best economics. I...
