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

As for the T-Bevel, it's of decent quality and works as expected. I can easily transfer known angles with it. Five stars for that aspect alone. As for the digital protractor, however, it's only worth one star to me. To test the accuracy of the protractor's functionality, I zeroed it on a known flat surface and then compared it to two known 90 degree angles - one was a carpenter's angle and the other was my Jevon 3D angle. Both fluctuated constantly within half a degree, plus or minus. Every time I reset the zero point and remeasure the angle of the known surface, it still shows as zero. I also verified that the reference surface is actually flat by trying to insert a feeler gauge between a perpendicular carpenter's square and a flat surface (granite countertop) to make sure there are no bumps. The caretaker square and the 3D square reflected the same 0 degrees. But when I went back to measure the flat surface angle, it was off again. A bit of math and a half degree on the length of the blade would mean there should be a gap of about 0.05 inch somewhere if that is correct, both measuring 0 degrees and measuring 90 degrees. I even manage to stick a .0015 dipstick in one of them.