The octant has an ebony frame and limb with a brass index arm and fittings, a detached wooden handle, and an inlaid ivory plate on the crossbar. The tangent screw and the clamping screw are located on the back of the index arm. The octant has three index shades, two red, and one green. Index-glass adjustment is made by a screw, and horizon glass by an extended lever and clamping screw operated from beneath the sight vane. The octant also has a single lens magnifier attached on a 76mm swivelling arm. The sight vane has two pinholes and a swivelling shutter. A threaded brass socket on the back of the crossbar used for fitting a stand is perhaps a later addition. The octant is contained in a polished mahogany keystone box.

The instrument has an inlaid ivory scale from -2° to 108° by 30 arcminutes, measuring to 90°. The octant has an ivory vernier measuring to 1 arcminute, with zero at the right.

Peter Dollond patented the horizon-glass adjustment (no. 1017 of 1772). The scale mark is for Edward Pritchard, an apprentice of Ramsden.