The octant has a mahogany frame and limb with a brass index arm, fittings, and a brass stop for the index arm. The inlaid ivory plates on the crossbar and on the back of the frame have been replaced by inlaid brass plates, and a brass strip has replaced the scale. There is no tangent screw and the clamping screw is on the back of the index arm. The octant has two red socket shades both red. Index-glass adjustment is made by a screw, and both horizon glasses by levers, wing nuts, and clamping screws. The index glass, horizon glass, clamping screws, and a wing nut are missing. The sight vane has two pinholes and a swivelling shutter, and the back sight vane has one pinhole. The lower half of the index arm is decoratively engraved, including a three-mast vessel. The outer ends of the limb have been sawn off and the centre strut, which once contained a pencil or screwdriver, has been removed. Two brass feet are missing from the frame. The octant has no box.

The inlaid ivory scale has been removed. The ivory vernier is graduated to 1 arcminute, with zero at the centre.

This instrument was adapted to commemorate the voyage of HMS ‘Deptford’ in 1761-62, in which John Harrison’s son William took part to test Harrison’s fourth timekeeper H4 of 1759.