This instrument is a folding arm protractor. It is used for measuring angles on the vertical and horizontal planes. The two folding arms have small metal support springs where they are attached to provide support and the other ends have pins with which to mark particular points. A screw mechanism on the rim allows fine tuning of plotting. Chadburn Brothers were fine instrument makers of Sheffield making optical and nautical instruments during the 19th century. This item was donated by a local resident whose grandfather Carl Spence was a bridge builder who worked on the Warrnambool Breakwater extension c 1919. This item has scientific significance which is possibly linked via the owner to one of Warrnambool's most well known landmarks.Brass, circular instrument with fold out sections which are hinged and a movable section. The circular part is marked in degrees around the circle. Notches on inner rim at 90 degrees intervals. Chadburn ,Brothers Sheffield. Graduated scale measuring 360 degrees.warrnambool, warrnambool breakwater, folding arm protractor, brass folding arm protractor, chadburn brothers, carl spence warrnambool