what is it

could be a tool used in the printing trades.

Its a square used to determine run and rise of stair treads.

a quarter & square?

-- If you can't fix it with a hammer, you've got an electrical problem!

I think it’s a quarter. Used to make arcs or complete circles. Expert craftsmen can use them for screwdrivers in an emergency. Full sets sell for about $10 and come in a handsome roll.

Is it a square designed for 1/12th models?

Bob

-- A mind, like a home, is furnished by its owner

A measuring tool for sewing…

-- Never board, always knotty, lots of growth rings

How about a tenon square, for timber construction?

-- Mike in Manchester, NH---Unpleasant tasks are simply worthy challenges to improve skills.

looks like kindlingmaker got it right,it’s a lufkin tailors and dress makers square,shinju