The octant has a mahogany frame and limb with a brass index arm, fittings, and a stop for the index arm. It also has inlaid ivory plates on the crossbar and on the back of the frame. There is no tangent screw, and the clamping screw is on the back of the index arm. The octant has three socket shades in green, orange, and red, with the top socket broken. Index-glass adjustment is made by a screw, which is missing, and both horizon glasses by levers, wing nuts and milled clamping screws.

The sight vane has two pinholes and a swivelling shutter, whereas the back sight vane has one pinhole. The octant is contained in a keystone box with a stepped lid that is painted black on the outside.

The lid contains a trade label for ‘Benjamin Cole, next the Globe Tavern in Fleet Street, London’. The bottom of the box is marked in ink, ‘Hadley’s sea octant otherwise quadrant invented 1731’.

The instrument has an inlaid ivory scale in two sections (joined at 45°) from -5° to 95° by 20 arcminutes measuring to 94°.The octant has a brass vernier measuring to 1 arcminute, with zero at the centre.