A B C OF THE STEEL SQUARE 



49 



dotted line, ce, shows the edge of the plank from 

 which the string is cut, and h shows the fence, 

 a shows the bottom tread and riser. In this ex- 

 ample the riser shows the same height as the riser 

 above it, namely, 7 inches. This is wrong, as the 

 first riser should always be cut the thickness of 



Fig. 25. 



the tread less than those above it, as shown by 

 the dotted lines on the bottom of the string, 

 then when the tread is in place it will be the 



Fig. 26. 



same height from the top of the floor to the top 

 of the first tread, that the top of first tread is 

 to top of second one and so on. 



Suppose we wish to lay out a rafter having 

 eight inches rise and twelve inches run. Set the 



