50 A B C OF THE STEEL SQUARE 



fence at the 8" mark on the blade, Fig. 26, and 

 at the 12" mark on the tongue, clamping it to 

 the square with l 1 /^" screws. Applying the 

 square and fence at the upper end of the rafter 

 we get the plumb-cut P at once. By -applying 

 the square as shown twelve times successively the 

 required length of the rafter and foot-cut B is 

 obtained. In this case the twelve applications of 

 the square are made between the points P and B. 

 Run and rise must also be measured be- 

 tween these points. If run is measured from 

 the point B, which will be the outer edge of the 

 wall plate, it will be necessary to run a gauge 

 line through B parallel to the edge of the rafter, 

 and subtract a distance from the height of the 

 ridge to give us the correct rise. The square 

 must then be applied to the line L. A rafter of 

 any desired rise and run may be laid off in this 

 manner by selecting proportional parts of the 

 (rise and run for the blade and tongue of the 

 square. For a half -pitch roof use 12 in. on both 

 tongue and blade, for a quarter-pitch use 6 in. 

 and 12 in., for a third-pitch use 8 in. and 12 

 in., etc. The terms half-pitch, quarter-pitch, 

 etc., refer to the height of the ridge expressed 

 as a fraction of the span. 



The line L is supposed to represent the path 

 of the fence as it is slid along the edge of the 



