Maybe I used it wrong so my result wasn't perfect. Maybe the wood is warped. I was making a spice cabinet and only made 2 corners at a time and they didn't align properly when I made the other 2. In theory, if 2 corners form 90 degree angles and two opposite corners form 90 degree angles, they should be square. when they are merged. I'm not a professional carpenter so this most likely didn't work perfectly due to user error. The final draft turned out to be "good enough," so no complaints.