Hi everyone, this is a fairly basic thing to do, yet, many may not know this little trick. Whether you have a combination square, carpenters square, machinists square, etc., they can all be checked to tell how square they truly are with a very simple method. Find a piece of plate, sheet metal, flat bar, or other type of material that has a straight edge that you can put the square against and draw a line from. Flip the square over on that same edge and hold the blade of the square on the same line that you just drew, if the blade of the square is still parallel to the line that was drawn, the square is indeed square. Regards, aevald