On Jan 7, 3:40 pm, Fred McKenzie wrote:

I once had an automotive tachometer that hooked between the engine's
points and ground, and was calibrated in RPM. I do not recall, but
there may have been separate scales for 6 and 8 cylinders.

The Mad Scientist still hasn't told us his application. Something like
that could work if he wanted to measure a stable frequency but it
would be of no use if he wanted to play music into it and have it
dance to the notes. '

There is no point to this discussion. If he doesn't want a frequency
meter for a single, continuous tone, he's barking up the wrong tree.
His meter won't provide a useful display no matter what.