Figure 2-12.-Types of protractors.
Protractors used by the EA are usually graduated
in increments of 1/2°. By careful estimation,
angles of 1/4° may be obtained. Protractor
numbering arrangement varies. Semicircular
protractors are generally labeled from 0° to 180°
in both directions. Circular protractors may be
labeled from 0° to 360° (both clockwise and
counterclockwise), or they may be labeled from
0° to 90° in four quadrants.
Protractors should be stowed and cared for
in the same manner as triangles.
The ADJUSTABLE TRIANGLE, shown in
figure 2-13, combines the functions of the triangle
and the protractor. When it is used as a right
triangle, the hypotenuse can be set and locked at
any desired angle to one of the bases. The
transparent protractor portion is equivalent to a
protractor graduated in 1/2° increments. The
upper row of numbers indicates angles from 0°
to 45° to the longer base; the lower row indicates
angles from 45° to 90° to the shorter base. By
holding either base against a T square or
straightedge, you can measure or draw any angle
between 0° and 90°.
The adjustable triangle is especially help-
ful in drawing building roof pitches. It also
allows you to transfer parallel inclined lines
by sliding the base along the T square or
Irregular curves (called FRENCH CURVES)
are used for drawing smooth curved lines
that are not arcs or circles, such as ellipses,
parabolas, and spirals. Transparent plastic french
curves come in a variety of shapes and sizes.
Figure 2-13.-Adjustable triangle.