The octant has an ebony frame and limb with a brass index arm, fittings, and a brass stop for the index arm. It also has inlaid ivory plates on the crossbar and on the back of the frame, which is now missing. There is no tangent screw and the clamping screw is located on the back of the index arm. The octant has two socket shades in green and red. The index glass mount is hinged, with perpendicular adjustment by an adjacent capped thumbscrew. The mount is fitted on a short arm for parallel adjustment by a capped thumbscrew. Both horizon glasses are adjusted by screws. The sight vane has two pinholes and a red lever-operated shaded shutter and the back sight vane has one pinhole. A pencil or screwdriver is missing from the crossbar. The octant is contained in a polished stepped oak box, with ‘T.P.B’ cut in the top of the lid.

The instrument has an inlaid ivory scale from -2° to 99° by 20 arcminutes, measuring to 91°. The octant has an ivory vernier measuring to 1 arcminute, with zero at the right.