Let's play a tool guessing game.

What is it?

What is it's function?

Does this help?
Where is that Master detective,
Tom Brown?

I believe that this is a Starrett Vibrometer Tester of Amplitude of Vibration

Starrett No. 196 Universal Back Plunger Dial Test Indicator !

Tom hit it! Often used as a wear detector on rotating machinery.

Wow! you guys are great. Now, who would buy it?

I think it would have found use in the aeronautical field or any other field to test shaft vibration for critical applications. I believe these tests are done with lasers today?

The "Vibrometer" is still in a recent Starrett catalog. I believe it is used by stationary engineers on generators and other large rotating machinery to check for bearing wear and balance condition without an expensive and time-consuming teardown. And, yes Roger, lasers are used for the same purpose in the aviation industry!

Regards,
Bob (A&P)