Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 67
that if A D be the half, third,5 60 DRAWING INSTRUMENTS. or fourth part of A B, then D E will be a half, third, or fourth part ofB C ; and the same holds of all the rest. Hence, if D E be the chord,sine, or tangent of any arc, or of any number of degrees to the radius A D,then B 0 will be the same… … Fig. 151. be observed that all measures are to be taken from the inner lines, since these only run accurately to the centre. On the scale in common boxes of drawing instruments, the edges of the sides are divided as a protractor (Fig. 84) forthe laying out of angles. The ordinary pro-tractor…
Mechanical drawing
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