Should have read the reviews before ordering but didn't. Indeed, how difficult is it to make an accurate protractor in the 21st century? how could you screw it up Ask for common tools. Immediately after opening, I set the protractor to 45 and then to 90 degrees as a test. At 90 it is very obvious that the device is off by a few degrees (at 90 it is 3 degrees in focus). If you're trying to use this for work that requires precision, you're going to be out of luck. I was planning on using it to measure angles for trim pieces on a miter saw. If you could "evaluate" it it might almost be helpful, or if you knew how to correct inaccuracies, but you wouldn't have to.