old camera accessory4-ExposureMeter (Spring Hill, Somerville)

This stuff has been in my basement for over 15 years. I don't know exactly what it is.
This is in its original, but deteriorating, cardboard box. The box says "exposure meter." I did not remove the item from its foam packaging for a more complete photo.

Fair Chance Policy: I’ll wait before choosing a recipient to give more people a chance to reply.