The backstaff is made from a lignum vitae frame with boxwood arcs and crossbar, and brass rivets. There is an inlaid boxwood plate on the main strut. The staff also has a boxwood horizon vane and shadow vane. Decorative fleurs-de-lis are stamped in various places on the frame. The sight vane is a later replacement. The shadow vane may be an old replacement, or taken from another instrument.

The transversal scale on the thirty degree arc is from 0° to 25° by 5 arcminutes, and reads to 1 arcminute. The graduation on the sixty degree arc is from 0° to 65° by 1°, and on the outer edge has a scale for correcting for the Sun’s semi-diameter. The back of the thirty degree arc has scales for the Sun’s declination and the right ascension.

The backstaff was one of the principle instruments of navigation until the development of the octant in the 1730s. It was used facing away from the sun and required the measurement of a shadow cast onto the degree scale. They are usually made of wood.