Those modern tachs (I have a small autometer) are a different breed. They don't have a conventional D'Arsenval meter that reads to zero and has a magnetic coil. They are a type of stepper motor or something similar. My auto meter, if you rev it up and then kill the power, the needle stops wherever it was revving when you killed the power. Older tachs always drop to zero. I have no idea of the internal circuitry.
