The measuring instrument ...
at the head of the device appears (from the visible markings) to be a true micrometer, apparently American-made by the L. S. Starrett company of Athol, Mass.; measuring to the thousandth of an inch.
I did refer to the (apparent) recess in the nose of the spindle in an earlier post, and mentioned its possible relation to measurement of Berdan-anvilled cases.
There do appear to be other markings engraved on the body of the device, which, if deciphered, might well help solve the mystery...
mhb - MIke