The Spee Square is a three-sided, triangular shaped measuring tool, manufactured by Swanson Tool Co., Inc., that can be used to draw perpendicular lines on boards to be cut or to lay out angles for roofs, stairways, decks and other general construction. The tool is marked with degree gradations for fast layout and cutting of lumber without performing angle calculations. The Speed Square was invented in 1925 by Albert J. Swanson and has become a generic name for the family of triangular squares with pre-calculated markings. These tools are also called by their generic names, "rafter angle square". Modern Swanson Speed Squares can be differentiated from other rafter angle squares by their diamond shape cutout at the 3 1/2 inch mark.