Not to hijack this thread but it reminded me of the time back in the early 80's that I went to Sears to buy a framing square. I brought along my pencil and a piece of cardboard about 2'X3'. I laid the cardboard against the flatest and straightest objects I could find in the tool department which was a ground tablesaw table and fence. Using the method of aligning the short leg with the top edge of cardboard and drawing a 90 degree line tracing along the long leg , and the flipping the short leg over, and doing the same thing from the other side revealed that many of the top of the line Craftsman framing squares were close to 1/8" out of square. I must have checked 6 or 8 squares before I found one close enough to spend money on. The manager nervously allowed me to check them until I found the one I still have today. If he hadn't let me check them I definately wouldn't own a Craftsman framing square today.