On the back of the blade (Fig. 4) will be found the _board measure_, where eight parallel lines running along the length of the blade are shown and divided at every inch by cross-lines. Under 12, on the outer edge of the blade, will be found the various lengths of the boards, as 8, 9, 10, 11, 12, etc. For example, take a board 14 feet long and 9 inches wide. To find the contents, look under 12, and find 14; then follow this space along to the cross-line under 9, the width of the board; and here is found 10 feet 6 inches, denoting the contents of a board 14 feet long and 9 inches wide.
=To Find the Miter and Length of Side for any Polygon, with the Steel Square.= In Fig. 5 is shown a pentagon figure. The miters of the pentagon stand at 72 degrees with each other, and are found by dividing 360 by 5, the number of sides in the pentagon. But the angle when applied to the square to obtain the miter, is only one-half of 72, or 36 degrees, and intersects the blade at 8-23/32, as shown in Fig. 5.
[Illustration: Fig. 5. Use of Steel Square to Find Miter and Side of Pentagon.]
By squaring up from 6 on the tongue, intersecting the degree line at _a_, the center _a_ is determined either for the inscribed or the circumscribed diameter, the radii being _a b_ and _a c_, respectively.
The length of the sides will be 8-23/32 inches to the foot.
[Illustration: Fig. 6. Use of Steel Square to Find Miter and Side of Hexagon.]
If the length of the inscribed diameter be 8 feet, then the sides would be 8 × 8-23/32 inches.
The figures to use for other polygons are as follows:
Triangle 20-25/32 Square 12 Hexagon 7 Nonagon 4⅜ Decagon 3⅞
In Fig. 6 the same process is used in finding the miter and side of the hexagon polygon.
To find the degree line, 360 is divided by 6, the number of sides, as follows:
Now, from 12 on tongue, draw a line making an angle of 30 degrees with the tongue. It will cut the blade in 7 as shown; and from 7 to _m_, the heel of the square, will be the length of the side. From 6 on tongue, erect a line to cut the degree line in _c_; and with _c_ as center, describe a circle having the radius of _c_ 7; and around the circle, complete the hexagon by taking the length 7 _m_ with the compass for each side, as shown.