The sextant has an anodized brass three-circle pattern frame with a wooden handle. The tangent screw and clamping screw are positioned on the back of the index arm. The sextant has four shades, three grey and one orange, and three grey horizon shades. Index-glass adjustment is made by a screw and on the horizon-glass by a square-headed screw and a detached key.

Attached to the sextant is a magnifier on an 89mm 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 181 mm in length with an inverted image and two parallel cross wires. It is focused manually or by a milled screw and worm gear. An extra drawtube is 74 mm with two parallel cross wires, A second telescope is 83 mm with an erect image. The sight-tube is 80 mm in length with a red shaded eyepiece. Accompanying the instrument is a magnifying glass, an adjusting key, and a piece of chamois leather, the last of which is missing.

The artificial horizon consists of a rectangular cast-iron tray and a brass roof-shaped cover both black-lacquered. Two sides of the cover have clear glass panels, at an angle of 90°. A boxwood jar for storing the mercury (filled) when not in use.

The instrument has a polished brass limb with an inlaid silver scale from -5° to 150° by 10 arcminutes, measuring to 128°. 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 lined with green textile and with an ivory plate on the lid inscribed ‘J.C. Denniss Patent Sextant London’. The lid contains a trade label for J.C. Dennis, 122 Bishopsgate Street, London (1850-62).