The octant has an ebony frame and limb with a brass index arm, fittings, and a brass stop for the index arm, which is now missing. It also has inlaid ivory plates on the crossbar and on the back of the frame, which is missing. The tangent screw, with its knob missing is positioned on top of the index arm, and the clamping screw is on the back. The octant has three red socket shades. Index-glass adjustment is made by a screw and on the horizon glass, with its glass missing, by a lever, worm gear and a milled clamping screw. The back horizon glass is adjusted 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 pencil or screwdriver is missing from the crossbar. The octant is contained in a shaped wooden box, with a trade label for ‘J. M. and H. Cronmire, 10 Bromehead Street and Commercial Road East, London’ (1865-69).

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.