45.126Figure 2-12.-Types of protractors.Protractors used by the EA are usually graduatedin increments of 1/2°. By careful estimation,angles of 1/4° may be obtained. Protractornumbering arrangement varies. Semicircularprotractors are generally labeled from 0° to 180°in both directions. Circular protractors may belabeled from 0° to 360° (both clockwise andcounterclockwise), or they may be labeled from0° to 90° in four quadrants.Protractors should be stowed and cared forin the same manner as triangles.ADJUSTABLE TRIANGLESThe ADJUSTABLE TRIANGLE, shown infigure 2-13, combines the functions of the triangleand the protractor. When it is used as a righttriangle, the hypotenuse can be set and locked atany desired angle to one of the bases. Thetransparent protractor portion is equivalent to aprotractor graduated in 1/2° increments. Theupper row of numbers indicates angles from 0°to 45° to the longer base; the lower row indicatesangles from 45° to 90° to the shorter base. Byholding either base against a T square orstraightedge, you can measure or draw any anglebetween 0° and 90°.The adjustable triangle is especially help-ful in drawing building roof pitches. It alsoallows you to transfer parallel inclined linesby sliding the base along the T square orstraightedge.FRENCH CURVESIrregular curves (called FRENCH CURVES)are used for drawing smooth curved linesthat are not arcs or circles, such as ellipses,parabolas, and spirals. Transparent plastic frenchcurves come in a variety of shapes and sizes.142.318XFigure 2-13.-Adjustable triangle.2-11
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