The octant has a mahogany frame and limb with a brass index arm, and fittings. The back of the limb is also brass-covered and there is a wooden pad-shaped handle on the back of the frame. The clamping screw and tangent screw, which are both missing, are on a separate shoe fitted on the limb to the right of the index arm. The horizon glass and the back horizon glass both have their glass missing, but are now fitted with modern replacements. The octant has three red socket shades. The index-glass, the lower half of which is not silvered, is adjusted by a screw, and fitted with a Maskelyne flap. The horizon-glass is adjusted by a milled screw and a lever, wing nut and clamping screw, which is missing, and the back horizon-glass is adjusted by a 133 mm lever and two milled wheels, operated from below the telescope bracket. The threaded telescope brackets for fore- and back-observation are both fitted for correcting collimation error. Perpendicular adjustment is made on both by the rising piece and milled knobs, the forward of which is missing. The telescope for this octant is missing. Part of the frame near the lower shade-socket is broken. The octant is contained in a wooden keystone box with a stepped lid that has been repaired.

The instrument has a surface-mounted polished brass scale graduated from -4° to 94° by 20 arcminutes, measuring to 90°. The octant has a brass vernier measuring to 1 arcminute, with zero at the centre.

Peter Dollond patented the back horizon-glass adjustment (no. 1017 of 1772). By a second lever (249 mm) this glass can be swivelled 90° and brought into the same position as the horizon glass. The telescope was then placed in the lower position, the back glass adjusted, and reversed to its position for the back-observation. A sextant by Dollond with the same adjustment device is in the Whipple Museum of the History of Science in Cambridge, inventory number Wh.1292.