Bennett, J. and Johnston, S., The Geometry of War, 1500-1750 (Oxford, 1996)
65. A beautifully executed, specialist protractor, by a maker whose instruments often have military associations. There are basically two scales on the brass plate - an outer scale of degrees subdivided by diagonals, and an inner set of scales for drawing polygons of from three to sixteen sides. To draw any of these regular polygons, the radial arm is set to the successive positions marked for the figure in question and the sides drawn with the tangential arm.
Diameter: 132 mm
Inventory no. 54,619