and so on to the bottom of the figures.
To Find the Length of a Rafter.—For a roof with 1-6 pitch (or the rise 1-6 the width of the building) and having a run of 12 feet, follow in the rafter table the upper 1-6 pitch ruling, find under the graduation figure 12 the rafter length required, which is 12 7 10, or 12 feet and 7 10-12 inches.
For ½ pitch (or the rise ½ the width of the building) and run 12 feet, the rafter length is 16 11 8, or 16 feet 11 8-12 inches.
If the run is 25 feet, add the rafter length for run of 23 feet to the rafter length for run of 2 feet.
When the run is in inches, then in the rafter table read inches and twelfths instead of feet and inches. For instance:
If with ½ pitch the run is 12 feet 4 inches, add the rafter length of 12 feet to that of 4 inches, as follows:
| For run of 12 feet the rafter length is | 16 feet 11 8-12 inches. |
| For run of 4 inches the rafter length is | 5 8-12 inches. |
| Total | 17 feet 5 4-12 inches. |
The brace measure on these squares is along the center of the back of the tongue, and gives the length of the common braces as shown in [Fig. 11]. Examples are shown in the blade as at the point marked 24 30, which means 24 inches on the post and 18 inches on the beam or girt, which make the brace 30 inches long from point to point according to the rule given. An application of this rule is shown at [Fig. 12], where 36 inches are laid off on both post and beam, which gives the length of the brace from point to point 50.91 inches, or very nearly 4 feet 3 inches. Other dimensions are shown in the square. There is also a scale of one-hundredths, or one inch divided into 100 equal parts.
The octagon scale on this square runs along the middle of the face of the tongue, and is used for laying off lines to cut an “eight square” or octagon stick of timber from a square one.
