I got this at a yard sale . I can't figure out what it is used for. It has a federal increment gauge on top and inside is a circular magnet that is located above the hole in the bottom brass plate. All parts are brass. The magnet seems to be on a beam that moves and you get a reading on the gauge. What was this used to measure? Also have the original box and it looks like the boxes that federal sent there items out in so I believe this was made by the manufacture. The case to this is all bakelite plastic precision made and machine screws
