Quoting from the table of directions given in Sargent’s circular describing this square, we have, for rafter cuts, the following explanation: “This run of a rafter set up in place is the horizontal measure from the extreme end of the foot to a plumb-line from the ridge end—from A to B, Fig. 6.
“The rise is the distance from the top of the ridge end of the rafter to the level of the foot. From C to D, Fig. 7.
“The pitch is the proportion that the rise bears to the whole width of the building. The illustration, Fig. 8, shows one-third pitch; the rise of 8 foot being one-third of the width of the building.
“The cuts or angles of a rafter are obtained by applying the square so that the 12-inch mark on the body and the mark on the tongue that represent the rise shall both be at the edge of the rafter. The illustration, Fig. 9, shows 8 foot rise, the line A the cut for the ridge end of the rafter and B the cut for foot end.”
The portion of square shown at Fig. 10 exhibits the tool having on its face a table of the run, rise and pitch of rafters, being specially figured for this purpose, and shows the measure of the rafter for any one of seven pitches of roof based upon the length of the horizontal measurement of the building from the center to the outside.
The following table, which was prepared especially for this square, shows the manner of working the square:
The rafter table and the outside edge of the back of the square, both on body and tongue, are in twelfths. The inch marks may represent inches or feet, and the twelfth marks may represent twelfths of an inch or twelfths of a foot (that is, inches) as a scale. The rafter table is used in connection with the marks and figures on the outside edge of the square.
At the left end of the table are figures representing the _run_, the _rise_ and the _pitch_.
In the first column the figures are all 12, which may be used as 12 inches or 12 feet, and they represent a _run_ of 12.
The second column of figures is to represent various _rises_.
The third column of figures in fractions represents the various _pitches_.
These three columns of figures show that a rafter
with a run of 12 and a rise of 4 has 1-6 pitch,
with a run of 12 and a rise of 6 has 1-4 pitch,