Protractor.

Patent for a new and improved protractor. This design "is to make a protractor or plotter by which may be calculated the length of the base, perpendicular, and hypotenuse of a right-angled triangle where the latitude and departure or the altitude and depression are given" (lines 15-20). To this end, it consists, "with the semicircular protractor provided with a rectangular opening the edges of which are graduated, and centrally-pivoted vernier, of the departure-scale arranged to move up or down within the said rectangular scale within the semicircular scale" (lines 6-12)