I believe the semiconductor tach I've got in my daily-driver '67 Falcon is an Electro-Voice, sold under the Dixson name; need to look at it tomorrow.
I used to wonder how J.Otto Crocker came up with his famous timers that were accurate to .001 seconds, to use in-the-middle-of-nowhere, such as Bonneville. Finally located the answer in an old Hot Rod Magazine article- back in 1934 he perfected his scheme of using a tuning fork as the time base. [I have to assume the fork was in an evacuated container to eliminate varying air density concerns?]