From the Manufacturer
The Swanson Tool SO101 7-inch Speed Square is a popular pocket-sized square that incorporates features of the framing square, tri, miter, and protractor squares. Common rafter and hip/valley rafter scales permit one-number references for all cuts. The square is merely rotated to the proper roof pitch value on teither scale to assure the correct angle cut. The slot along the scales will accommodate an adjustable locking pin for repetitive cuts using any 1/4-inch bolt and nut. Comes with a handy, 62-page pocket sized booklet that provides vital instructions, reference diagrams, and tables for the construction of roofs and stairs.