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My first guess was a fancy angle finder. The degree wheel has percent and degrees engraved on the end. No brand name. Upon closer examination, there is a small peep hole on one end, and a 45 degree mirror under the bubble in the square tube. The other end is open with a thin horizontal brass flat wire. It is something you'd look through. Engraved on the side THS56-0612. A knob where it looks like you could attach a lanyard. Black anodized finish, looks like decent quality for Japanese goods.
Steve