Tangent: In the late 50s my dad was sales manager at Electro-Voice, and EV once upon a time made tachometers that worked with an inductive pickup. With each new tach came a little "tuning fork"-like device that was calibrated to wiggle just-so at a specific RPM - and so the tach could be calibrated.
I discovered, for instance, that the bushing bearings in the 47cc go kart engine (which was originally limited to 4,800 rpm) lived for a few weeks of regular 8k runs through the subdivision. I also discovered what a seized bearing does...or doesn't do.
Hijack over.