Review on Accurate and Easy-to-Use General Tools 828 Digital Protractor for Precise Angle Measurements by Matthew Maxwell

you don't have a fixed measurement for like a square). Unfortunately, it easily loses its angle measurement as the blade rotates, and you have to zero it before each measurement. To zero the instrument, place it on a flat surface with the blade closed and press the reset button. If you then rotate the blade 180 degrees (careful, as the plunger re-enters the groove the unit tends to lose angle) you get an idea of the accuracy (my readings ranged from 179.7 to perfect 180). - this means you can trust the readings within 0.5 degrees and are within the 0.3 degrees stated by the manufacturer). If the blade rotates, the device will most likely lose its angle display and you will have to start over. This is especially true if you pull out the blade while spinning, which is what you need to do to use the device as an angle device. This helps turn the knob far enough to create a bit of tension. There's a hold button to hold the reading, which is useful as turning the knob down is likely to throw off the protractor. When measuring angles, several measurements should be taken before believing the result, and when fixing angles, a small protractor should be used to get an approximate double check of the angle. It would be a great tool if it retained its calibration after zeroing and if it didn't easily lose the angle gauge as the blade rotated.