The octant has an ebony frame and limb with a brass index arm and fittings. It also has a brass stop for the index arm and inlaid ivory plates on the crossbar and on the back of the frame. The tangent screw is positioned on top of the index arm and the clamping screw is on the back. The instrument has three index shades, two red and one green. There are no horizon shades and the socket hole has been filled in. Index-glass adjustment is made by a screw and on the horizon glass by a lever, wing nut and a milled clamping screw. The sight vane has two pinholes and a swivelling shutter. A pencil or screwdriver is missing from the crossbar. The octant has no box.

The instrument has an inlaid ivory scale from -2° to 99° by 20 arcminutes, measuring to 89°. The octant has an ivory vernier measuring to 1 arcminute, with zero at the right.

No other instrument by Alexander of Yarmouth is recorded; he may have been an owner or a retailer.