There is more than one thread on this topic. I found that, when adjusting the bevel either to an angle different from 0 degrees or back to zero, the back bevel lock knob needs to be tightened first as that is where the stop is located. Once the back knob is tightened, tighten the front knob without putting any stress on the frame. Pushing down on the saw's frame in front at all, will move the front out of square compared to the back. Once I figured that out, I had no more problems. However, there is a way to adjust the stop in the back of the saw and either service can direct you or one of the several threads out there concerning this topic has direction. I don't remember all the thread names, but a patient search with words like "zero", "perpendicular to the sole plate", etc. should help you find them.