ure a board 14' long, and 11" wide,--under the
figure 12, find 14 (length of the board); to the left of this, under
11 is the number 12.10; 12' 10" is the board-measure of the board in
question. Since a board 12' long would have as many board feet in it
as it is inches wide, the B. M. is omitted for 12' boards. Likewise
a board 6' long would have 1/2 the number of board feet that it is
inches wide. If the board is shorter than the lowest figure given
(8) it can be found by dividing its double by 2.; e. g., to measure
a board 5' long and 9" wide, take 10 under the 12, run to the left of
the number under 9, which is 7' 6": 1/2 of this would be 3' 9", the
number of board feet in the board.

If the board to be measured is longer than any figure given, divide
the length into two parts and add the result of the two parts obtained
separately. For example, for a board 23' long and 13" wide,--take
12'x13" = 13'; add to it, 11'x13" = 11' 11"; total, 24'11".

[Illustration: Fig. 197. Steel Square with Rafter Table.]

A good general rule is to think first whether or not the problem can
be done in one's head without the assistance of the square.

The table is made, as its name, Board-Measure (B. M.) implies, for
measuring boards, which are commonly 1" thick. For materials more than
1" thick, multiply the B. M. of one surface by the number of inches
thick the piece measures.

The rafter-table is found on the back of the body of the square, Fig.
197. Auxiliary to it are the twelfth inch graduations, on the outside
edges, which may represent either feet or inches.

[Illustration: Fig. 198. The "Run" and "Rise" of a Rafter.]

By the "run" of the rafter is meant the horizontal distance when it is
set in place from the end of its foot to a plumb line from the ridge
end, i. e., one half the length of the building, Fig. 198. By the
"rise" of the rafter is meant the perpendicular distance from the
ridge end to the level of the foot of the rafter. By the pitch is
meant the ratio of the rise to twice the run, i. e., to the total
width of the building. In a 1/2 pitch, the rise equals the run, or 1/2
the width of the building; in a 1/3 pitch the rise is 1/3 the width
of the building; in a 3/4 pitch the rise is 3/4 the width of the
building.

[Illustration: Fig. 199. Lumberman's Board Rule.]

To find the length of a rafter by the use of the table, first find the
required pitch, at the left end of the table. Opposite this and under
the