What Are All Those Numbers? The Steel Square, by Gilbert Townsend. American Technical Publishers, 1155 W. 175th, Homewood, IL 60430. 1947. 172 pages $8.82 postpaid. Dialing for Rafters Dial-a-Length Rafterule. Craftsman Book Co., 6058 Corte Del Cedro, Carlsbad, CA 92009. $9.50. by Paul Hanke "Rafterule" is a device consisting of two circular plastic disks with a clear hairline arm, all of which rotate around a center rivet. To determine the lengths of common or hip and valley rafters, you simply set the red pointer arrow on the roof pitch (say, 5/12), rotate the hairline to the building width (28 feet, for example), and read the rafter length (15'2") on the appropriate table through a window in the