HOW ACCURATE ARE THE FACTORY TACHS

Anything that uses a mechanical meter is subject to a fair amount of inaccuracy, especially as old as these are. There are LOTS of room for error, including temperature and humidity changes, variations in the circuit components, as well as changes in the circuit components do to aging, temperature, etc. And the meter itself. Just static electricity on the face can give problems. Should I bother to mention these get beat to $hxt with bumps and the rest of it? Some? Many? newer tachs like autometer do not use the same kind of meter movement as "in the old days." I would guess Autometer uses a stepper motor movement, as when you shut them off, they "stick" at whatever RPM the engine was turning.