I purchased this T-square and the one I got did not have a perfect right angle. The T-top is made out of wood as is the straight edge piece. These two pieces of wood are held together by 5 small screws. The low grade wood used in making this t-square will have a tendency to warp. The screws in the one I purchased weren't all uniform to begin with so that leads me to think that either the machines used to make them are imperfect or the workmanship is lacking. (By the way, I bought mine at Staples and ALL of the T-squares had the same issues with the screws.)If you're just look to make a straight line fairly perpendicular to an edge, then it's okay for that. If you're looking for something with a perfect right angle, I recommend staying away from this item.