graduation on the edge representing the run in feet, will be found
the length of the rafter; e.g., a rafter having a run of 12' with a
1/4 pitch, is 13' 5" long, one with a run of 11' and a 1/3 pitch,
is 13' 2-8/12", one with a run of 7' and a 5/8 pitch, is 11' 2-6/12"
long, etc.

When the run is in inches, the readings are for 1/12 of the run in
feet: e.g., a rafter with a run of 12" and a 1/4 pitch is 13-5/12",
one with a run of 11" and a 1/3 pitch, is 13-3/12". Where the run is
in both feet and inches, find the feet and the inches separately; and
add together; e.g., a rafter with a run of 11' 6", and a 1/2 pitch, is
15' 6-8/12" + 8-6/12" = 16' 3-2/12".

[Illustration: Fig. 200. Try-Square. Fig. 201. Miter-Square. Fig. 202.
Sliding-T Bevel.]

The _lumberman's board-rule_, Fig. 199. To measure wood by it, note
the length of the board in feet at the end of the measure. The dot
nearest the width (measured in inches) gives the B. M. for lumber 1"
thick.

The _try-square_, Fig. 200, which is most commonly used for measuring
the accuracy of right angles, is also convenient for testing the
width of a board at various places along its length, for making short
measurements, and as a guide in laying out lines with a pencil or
knife at right angles to a surface or edge. The sizes are various and
are indicated by the length of the blade. A convenient size for the
individual bench and for ordinary use has a blade 6" long. It is also
well to have in the shop one large one with a 12" blade.

[Illustration: Fig. 203. Using the Try-Square.]

[Illustration: Fig. 204. Scribing with Knife by Try-Square.]

In testing the squareness of work with the try-square, care must be
taken to see that the head rests firmly against the surface from which
the test is made, and then slipped down till the blade touches the
edge being tested, Fig. 203. The edge should be tested at a number
of places in the same way: that is, it should not be slid along the
piece. The try-square is also of great use in scribing lines across
boards, Fig. 204. A good method is to put the point of the knife at
the beginning of the desired line, slide the square, along until it
touches the knife-edge; then, resting the head of the square firmly
against the edge, draw the knife along, pressing it lightly against
the blade, holding it perpendicularly. To prevent the knife from
running away from the blade of the try-square, turn its edge slightly
towards the blade.

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