The octant has an ebony frame and limb with a brass and black-lacquered index arm and fittings. It also has inlaid ivory plates on the crossbar and on the back of the frame, which are both loose. The tangent screw and clamping screw are positioned on the back of the index arm. The octant has three index shades, two red and one green. Index-glass adjustment is made by a fixed milled key and on both horizon glasses by levers, worm gears and milled clamping screws. The sight vane has two pinholes and a swivelling red shade, whereas the back sight vane has one pinhole. An ivory-capped pencil head is fitted in the crossbar. The octant is contained in a shaped box with a stepped lid, with trade labels for George Whitbread, 2 Grenada Terrace, London (1842-74), and for the Magazzino di Carlo Ruspini, Strada Banchi and Strada Orefici, Genova.

The instrument has an inlaid ivory scale from -2° to 100° by 20 arcminutes, measuring to 90°. The octant has an ivory vernier measuring to 1 arcminute, with zero at the right.