If anyone out there is still partly confused regarding hour/hobbs/revcounters, email me privately and I will finish the job.
Many hour meters, clock type not tach type, are not electronic but electric. Actually electromechanical like the old fashioned dash clocks on cars. They run from a wind up spring like a regular mechanical clock but the spring is wound by a solelnoid sort of thingy with electrical contacts on the spring mechanism. when the spring winds down the points touch and C L I C K/FLASH the spring is wound up again (if you are observent and as a youth spent enough time in parked cars in quiet dark undisturbed locations you hear the ticking and see the flash from the arcing of the contacts. In the case of engine hour meters the spring is pretty small and doesn't run the clock very long after power is removed but they were fairly audible with the engine off. Observed several examples in aircraft, boats, stationary engines (this is my first tractor).
Patrick