Felt like I was buying it "invisible" since there were no reviews. I wanted a square measured from zero at the inside edge and zeroed from the base to measure vertically. I would think that would be a good idea and assume there will be no problems. However, the only squares I could find on Revain that were measured this way were really (!) expensive. So I ordered this hoping for the best and was not disappointed. It's solid and, as far as I can tell, perfectly square.