The sextant has a black-lacquered brass straight-bar pattern pillar frame, with twenty pillars, a protective frame over the fittings and mounts, and a wooden handle. The tangent screw and clamping screw are positioned on the back of the index arm. The sextant has four shades, two red, one orange, and one green, and three horizon shades in red, orange, and green. Index-glass adjustment is made by a screw and on the horizon glass by a capstan screw and a capped screw.

Attached to the sextant is a magnifier travelling on a worm screw with a milled knob. There is also a threaded telescope bracket with perpendicular adjustment made by a rising-piece and a milled knob. The telescope is 173 mm in length with an inverted image and four cross wires. A second telescope is 145 mm with an inverted image and four cross wires. A third telescope is 65 mm with an erect image. It has a rotating shaded eyepiece with three shades, two red and one green, an adjusting pin, and a piece of chamois leather. The sextant is contained in a mahogany keystone box, with a trade label in the lid for J.D. Potter, 31 Poultry, successor to R. Bate (1851-80). Illegible pencilled calculations are found in the lid. The box is fitted in a leather carrying case with a leather strap.

The instrument has a polished brass limb with an inlaid silver scale from -2° to 139° by 15 arcminutes, measuring to 123°. The sextant has a silver vernier measuring to 15 arcseconds, with zero at the right.

Captain (later Admiral) Robert Fitzroy, the original owner, commanded the survey vessel ‘Beagle’ on two major voyages, from 1828-30 and 1831-36. John Lort Stokes (1812-85) served under Fitzroy on both and himself became a notable surveyor.

The serial number ‘2029’ indicates the year of manufacture as being around 1831, which suggests that Fitzroy bought it for the second ‘Beagle’ voyage, during which he gave it to Stokes.

Edward Troughton patented the pillar and plate frame (no. 1644 of 1788).