mouth . Plumb cut of hip/valley rafters The plumb cut of the hip/valley rafter is expressed in the formula. The level cut is the complementary angle or 90° minus the arc tan. Irregular hip/valley rafters The only Framing Square that has tables for unequal pitched roofs is the Chappell Universal Square, (patent #7,958,645). There is also a comprehensive rafter table for 6 & 8 sided polygon roofs (first time ever on a framing square). The traditional steel square's rafter table (patented April 23,1901) is limited in that it does not have tables that allow for work with unequal pitched roofs. Irregular hip/valley rafters are characterized by plan angles that are not equal or 45°. The top plates can be 90° at the outside corners or various other angles. There are numerous irregular h/v roof plans. Carpenter's square In carpentry, a square is a guide for establishing right angles (90° angles) or mitre angles, usually made of metal. There are various types of square, such as speed squares, try squares and combination squares. See also Trammel Punch Combination square Hip roof References Notes Bibliography Woodworking measuring instruments Dimensional instruments Woodworking hand tools Squares (tool) de:Zimmermannswinkel