It looks like part of an upside down Planimeter, though
I could be wrong.
The pin on the left side should be underneath. Does the disk rotate (though with the nut on its left end and the rust IDK how)? There are graduated engineering scales [0 to 120; 0 to 140; 0 to 60; I can see others] but how those are set or used IDK.
I could use more pictures, different faces, more data on what moves and what doesn't. It looks pretty rusty for a once "finely tuned" instrument.
A planimeter is a machine for determining area on a scaled paper drawing or map. Civil Engineers and Surveyors used them. In my early career I used a more modern steel one like the one below from about '83 to '87 and before Computer Aided Design, when everything went digital.
I have a plastic one I still know how to use (but don't):