The octant has an ebony frame and limb with a brass index arm and fittings. It has inlaid ivory plates on the crossbar and on the back of the frame. The tangent screw and clamping screw are located on the back of the index arm. The octant has three index shades, one of which is green, and the other two are missing. Index-glass adjustment is made by a screw and on the horizon glass by a lever and worm gear, a square-headed screw and a detached key. The sight vane has two pinholes and a swivelling shutter. An ivory cap for a pencil is fitted in the crossbar and the adjusting key is missing. One of the feet of the frame is an old replacement. The octant is contained in an oak keytone box, with a trade label for Duren and Costigan, 20 Burling Slip, New York (established in 1855) stuck over an unidentified trade label on the lid. There are also illegible pencil notes in the lid.

The instrument has an inlaid ivory scale from -2° to 107° by 20 arcminutes, measuring to 93°. The octant has a damaged ivory vernier measuring to 1 arcminute, with zero at the right.