FastCap’s Blue Dog Square allows you to scribe fast, accurate lines with ease and eliminates awkward alignment. It has 5 rotatable dogs built in the arms, allowing the edge of your material to be found instantly no matter how thick or thin it is. It can be used immediately on flat surfaces as the dogs return into the square when laying on any surface. The Blue Dog Square can even hang on vertical panels while resting on the dogs, providing an accurate reference line with no fumbling or tilting the square to rest on the edge. Just another great product developed by a carpenter on the shop floor.