ADJUSTABLE TRIANGLES

45.126 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. ADJUSTABLE 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 straightedge. FRENCH CURVES 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. 142.318X Figure 2-13.-Adjustable triangle. 2-11