The octant has a mahogany frame, boxwood limb with a brass index arm, fittings, and stop for the index arm. There is a an inlaid ivory plate on the back of the frame. There is no tangent screw and the clamping screw is on the back of the index arm. The octant has three socket shades, two red and one green. Index-glass adjustment is made by a screw and the horizon glass by a lever, wing nut and a clamping wing nut. The sight vane has two pinholes and a swivelling shutter. The back sight vane and glass, and the lower socket have been removed and replaced by an artificial horizon. The octant is contained in an oak keystone box.

The artificial horizon consists of a brass frame fitted to the front of the instrument, carrying a slightly curved spirit level. The bubble is reflected to the eye by a round lens and a special, adjustable mirror, mounted forward of the horizon glass, which reflects the Sun’s image onto the level.

The boxwood scale is in two sections (joined at 45°) from -5° to 95° by 20 arcminutes which is vice versa for the zenith distance, measuring to 92°. The ivory vernier (broken) displays a graduation to 1 arcminute, with, zero at the centre.