Auction find, else where in the sale were some watchmaker tools I can identify,   No idea on this one.  In the case is a heavy brass plate, threaded, used as a steady mount maybe.   Positive ID?

It might be some kind of navigation tool.  It looks like the adjusting screws might be used to compensate for drift.  Maybe used in conjunction with  a sextant or octant?

It looks like a planimeter. This is a rabbit hole you may not want to go down.

Mike