This tool is so inaccurate that it's frankly not worth owning. The adjustment knob is too loose and too easy to knock out of adjustment. There is no lock on it, so if the pen is nudged while trying to take a measurement, the link will disappear. The magnet is not fixed in the base at all, if desired it can be removed with your fingers. The metal base only has one screw in the middle, and it's one of those bases you find on a magnetic clip at an office supply store. The lines on the dragonfly do