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.