I recall when Padgett was repairing tachs, he used a graphite pencil to apply some graphite to a spot on the circuit board to tune the resistance. He said the factory reading was generally 200 RPMs off to read higher than actual engine speed. I do not recall where or how exactly but he had a meter reading the resistance and I saw it change to his desired spec.
This was close to 40 years ago and he's been gone 3 + years already. I did not commit the technical details to memory, obviously.
Hopefully someone else here has this knowledge.
And maybe this question would get more engagement in the Electrical forum.
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