Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 55
s coincide, the edge is straight;but if they disagree, the ruler is inaccurate, and must be rcjointed. Whenone ruler has been tested, others can be examined by placing their edges againstthe correct one, and holding them between the eye and the light. Triangles may be made of the same kinds of wood… … from 3 to 6 inches on the side. A larger size, from 8 to 10 inches long on theside, is convenient for making drawings to a large scale. In the smaller trian-gles circular openings are made in the body for the insertion of the end of thefinger, to give facility in sliding the triangle on the paper.…
Mechanical drawing
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