ORIGINAL: fizzwater2
You know, Barry, it might just be! It ought to be worth a fortune!
Even more archaic.. I have a Heathkit "Thumb Tach" that I built from a kit probably in 1973 or 1974... It works, but I wouldn't want to use it! Tiny meter, and no expanded scales - kinda hard to tell 20,000 RPM from 18,000 RPM on that one!
I remember them. I can't remember what I used for my F1's back in the 70's. I have been wanting a Master tach for Q40 and I am watching this one.