Simple device to help when measuring cabinet cases during assembly to ensure they are square.

The magnets hold the end of a tape measure in place, then hook the right angle over the corner of the case frame. The tape measure end will pivot and not fall off the corner of the cabinet so that you can measure the corner to corner diagonal to ensure the case is square.

The distance from the tape measure hook opening to the point of the cabinet corner is exactly 1", so whatever the tape measure reads subtract 1 and that is your measurement.

Created with 0.20mm swivel clearance so the average printer should not have trouble with this design. This makes the total inaccuracy of the play in the swivel less than half a millimeter, so all measurements are still very accurate.

Prints-in-place, with both parts printed together as one unit. The swivel disk is captive. After printing if the disk does not spin, just put a flat tool in the slot and a firm twist should break it free.

The inner part of the rotating disk is crenelated to reduce contact friction area and make it spin easier. This also helps make the device not bind after getting dusty in a woodshop.

After printing glue 2 6mmx3mm neodymium magnets in the round holes.
A few hundred of these magnets can be bought on amzn for just a few dollars, and they are very handy for projects like this.