Just set the dial and read off the answers. The Dial-A-Length Rafterrule determines the hip, valley, common and jack rafter length for any span with "saw cut" accuracy.
Gives plumb, level, and side cut data plus angle in degrees and minutes for 21 pitch setting. Scales graduated like any carpenters rule. Circular design gives accuracy to 1/16". Dial-A-Length Rafterrule produces nothing but correct answers