Tachometer question

KitCarlson said
It sounds like the gauge uses a stepper to drive the needle. That is typical for needle gauges in modern cars. They consist of a rotor with magnetic poles, and stator with coils. The coils are driven to step the rotor with a pulse. The electronics initializes the zero position, then steps and micro-steps for desired reading based on RPM. The movement does a fixed value of degrees movement per step, so the movement does not need calibration.

If this is how the Autometer tach electronics work, I understand that there is no calibration needed, however, as you stated, the electronics re-establish zero whenever 12 volts is applied so the tach should be at zero with the ignition power on without starting the engine. Great description of how the tach works by the way!