Vertical lines are drawn by means of triangles. The tri- angles most generally used are shown in Figs. 3 and 4, each of which has one right angle. The triangle shown in Fig. 3
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has two angles of 45° each, and that in Fig. 4 one of 60° and one of 30°. They are called 45° and 60° triangles, respectively. To draw a vertical line, place the T square in position
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to draw a horizontal line, and lay the triangle against it, so as to form a right angle. Hold both T square and triangle lightly with the left hand, so as to keep them from slipping, and draw the line with the pen or pencil held in the right hand, and against the edge of the triangle. Fig. 5 shows the triangles and T square in position.
4. For drawing parallel lines that are neither vertical nor horizontal, the simplest and best way, when the lines are near together, is to place one edge of a triangle, as ab. Fig. 6, on the given line cd, and lay the other triangle, as B,
