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. The tangent screw is positioned on the top of the index arm, and the clamping screw (renewed by F. N. Adams) is on the back. The octant has three socket shades, one in green, and two in red. Index-glass adjustment is made by a screw. On the horizon glass it is made by a lever, worm gear, and a milled clamping screw and on the back horizon glass by a lever, wing nut, and a milled clamping screw. The sight vane has two pinholes and a swivelling shutter, whereas the back sight vane has one pinhole. A brass-capped screwdriver is fitted in the crossbar. The octant is contained in a stepped oak box.

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.