P. J. Ogle's Improved Protractor

Circular protractor with one straight edge, and two moveable rings (one with clamps) which rotate against the inner and outer scales. The inside ring measures 90° four times. The middle ring has North, South, East and West plates screwed on to it. The S plate has a vernier scale which bears upon the inner scale. Central diametrical bar engraved 0-7 inches in 1-inch steps left to right and 1/32-inch steps right to left.Outer ring has four lots of 90°. Made of white metal - either electrum or nickel, with engraved scales. Made by J DAVIS & SON, LONDON & DERBY, Diameter = 291mm.