The sextant has an anodized brass bell-pattern frame, with a grey-green finish and a wooden handle with a brass-lined hole for the locking mechanism. The tangent screw and clamping screw are positioned on the back of the index arm. The sextant has four green shades and three green horizon shades. Index- and horizon-glass adjustment is made by a square-headed screw, a detached key, and capped square-headed screws.

Attached to the sextant is a magnifier on a 95mm swivelling arm with a frosted glass shade. There is also a threaded telescope bracket in two parts, fitted for correcting collimation error. It has perpendicular adjustment made by a rising-piece and a milled knob. The telescope is 176 mm in length with an inverted image and four cross wires. An extra drawtube is 95 mm long with an inverted image and two parallel cross wires. A third telescope is 72 mm long with an erect image (star finder). The sight-tube is 82 mm in length and has two green shaded eyepieces, a patent greatest angle clamp screw, Heath’s patent definition shade, and a milled adjusting key. One part is missing, which is possibly a screwdriver.

The instrument is contained in a polished brass limb with inlaid silver scale from -5° to 155° by 10 arcminutes, measuring to 131°. The sextant has a silver vernier measuring to 10 arcseconds, with zero at the right.

The sextant is contained in a square fitted wooden box with a patent locking mechanism for securing the instrument when not in use. A white ivorine label on the side of the lid is marked, ‘Bell pattern Mark III sextant’. An inlaid brass plate on top of the lid is marked, ‘J. R. Grant’. The lid contains a National Physical Laboratory certificate of examination, dated 8 September 1917.

Heath’s patent definition shade was to prevent the eye being dazzled during an observation in bright sunlight.