starrett mystery tool

[achong]

found this in my grandfathers tools. he picked up lots of machinist stuff
from garage sales, and likely had no idea what it was either.

There is a red eraser head tip, and when you turn the shaft
the little dial rotates. I'm guessing it's some sort of
tachometer where you have to pull out your handy
pocket watch and do some math.

I have another one, slightly different in worse shape, and
if anyone has to have it...

 

[paulsomlo]

Yes, it's a tach - here's a video, at about the ten minute point he shows how to use it:

 

[achong]

thanks.

I guess tacking on a hall effect sensor is pretty cheap nowadays, but
at the patent date of 1905, electricity was still novel.