Cutting off the outside arrises to the gaged lines leaves an octagonal stick.
[Illustration: Fig.196.Back of Steel Square, Essex Board Measure.] The board-measure is stamped on the back of the blade of the square, Fig.196.The figure 12 on the outer edge of the blade is the starting point for all calculations.

It represents a 1" board, 12" wide, and the smaller figures under it indicate the length of boards in feet.
Thus a board 12" wide, and 8' long measures 8 square feet and so on down the column.

To use it, for boards other than 12" wide:--find the length of the board in feet, under the 12" marked on the outer edge of the blade, then run right or left along that line to the width of the board in inches.

The number under the width in inches on the line showing the length in feet, gives the board feet for lumber 1" thick.
For example, to measure 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.