Excerpt from Instructions for Using Dolman's New Decimal Scale Measure Protractor This protractor is a semi-circle with the semi-circumference of the pro tractor graduated 90 degrees from OM line to the right, and left to the bottom line DD of the protractor. The om, or meridian line, meets bottom line, DD, at the middle, and in the centre of the small semi-circle and at right angles to line DD.
The two arms, bb, bb, must be fastened by a needle at the intersection of lines DD and O. M. In the small semi-circle. A parallelogram two by four inches, is cut out of the middle of the protractor parallel to sides LL, LL and DD, DD, and from equi-angular parallels, and by revolving the protractor one-half around, using the needle as a pivot, a four inch square, and a circle can be formed with a common centre to square and circle. The movable bar, DD, moves parallel to bottom line, DD.
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