Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 66
theodolites andsurveying instruments. The sector in its oldform carried several scaleson its faces. As given inFig. 149, there are onlydouble scales starting fromthe centre joint, which,without drawing, may beiipplied to the solution of problems on similar triangles. Let the lines A B, A C,… … Fig. 149.
Mechanical drawing
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