A friend recently bought a used tachometer (rev counter) from a well known auction site, and fitted it in his permit aircraft for a ground run to see if it worked.
The tacho appears to be the AC/Mitchell mechanical type often used on Lycomings, with a speedometer-type cable input on the back and a row of numbers to show accumulated hours, based on an assumed cruise RPM.
https://www.aircraftspruce.com/catal...mech_tachs.php
When doing the ground run, the 'hours' started building up at an alarming rate. After removal and dismantling, it appears that a gear has been moved along a shaft and secured with a blob of epoxy to gear the hours readout to six times the normal rate.
Can you think of a legitimate reason to modify a tachometer in this way, as falsifying one's hours (e.g when working to a commercial licence) is the only reason that currently springs to mind?