If you don’t have a steady RPM, that indicates a problem with the encoder signal (TDC signal).
If you’re using a mag pickup, then the most likely cause of TDC signal problems is an incorrect mag pickup gap. It needs at least 0.5 V peak. (For example, we’ve noticed on at least one unit that we had to adjust the gap closer than what a Windrock encoder was using.)
If you’ve successfully taken data in the past and are now having problems, then it may be a problem with RF interference.
Looking on the Pulse, the LED should flash consistently with the RPM, and on the Lenz the LED should be synchronized. If it is not right on the Pulse, then there is a problem with the pickup or cabling. If the Lenz does not match the Pulse, then there is communication problem between the two.