Thanks to one of the many astute readers of a favorite site of mine "Bits and Pieces" I have a link to an auction site that gives more background on this object.
I think either gadget or doohickey is apt, though I am slightly in favor of doohickey. I found this for you at http://www.mjdtools.com/auction/graphics/s09/a218950.htm “An example of HALL’S PATENT COMBINATION TOOL as produced by the Boye Needle Company, Chicago, Illinois. This tool was patented on February 10, 1926.”
If I was interpreting the auction site correctly, they were suggesting it was worth $80-$160.
Another tag sale find that I couldn't leave without. Paid $1. The sellers didn't know what it is. I have some idea, but the challenge I ask of you is not what it is, but how it is supposed to be used. Here are a few more images to help you guess:
The only text imprinted is "Boye Brand." It is possibly a level/miter of some kind and at 3" x 2.5" could have been meant for detail work, or work in a small scale. There is also this swing out arm that lines up with one edge...
It looks like a handy tool, but it leaves me with a lot of unanswered questions. Please leave your guesses, or the explanation in the comments.