I bought this tool because I made a lot of corners when making furniture and flower pots. Try it on two different crop squares and they both came out at exactly 90 degrees. I have three plastic corners that I use - these are 45, 30 and 22.5. Checking the tool on them gave the following: 45 = 44.1, 30 = 29.4, 22.5 = 22.4. Testing with a Swanson metal square showed that 45 angles measured 44.1 at each angle. From these measurements it follows that the tool tends to be on the low side of theβ¦