The octant is made from a mahogany frame and limb with a brass index arm and fittings. The octant has a brass stop for the index arm and inlaid ivory plates on the crossbar and on the back of the frame. There is no tangent screw and the clamping screw is missing on the back of the index arm. The octant has three socket shades in red, orange, and green. Index-glass adjustment is made by a screw and on both horizon glasses by levers, wing nuts and milled clamping screws. The sight vane has two pinholes and a swivelling shutter; the back sight vane has one pinhole. A brass-capped screwdriver is fitted in the crossbar. The octant is stored in a stepped oak box, containing in the lid a handwritten label ‘Father from Francis Isabel Gordon Pauline 8th De. 1907’

The instrument has an inlaid ivory scale from -5° to 95° by 20 arcminutes, measuring to 88°. The ivory vernier displays a graduation to 1 arcminute, with zero at the centre.

The maker’s name is inscribed on the index arm as ‘B. Martin, London’. This is Benjamin Martin (about 1705-82), a lecturer and scientific instrument maker based in London.