The sextant has an anodized 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, three red and one green, and three horizon shades, two red and one green. Index-glass adjustment is made by screw and on the horizon glass by capstan screws.

Attached to the sextant is a magnifier travelling on a worm screw with a milled knob. There is also a threaded telescope bracket attached with perpendicular adjustment by a rising-piece and a milled knob. The telescope is 129 mm in length with an inverted image and two parallel cross wires. A second telescope is 126 mm in length with an inverted image and two parallel cross wires. There is a third telescope which is 59 mm with an erect image. The sight-tube is 89 mm in length with a rotating shaded eyepiece with three blue shades and an adjusting key. The sextant is contained in a fitted polished mahogany keystone box with a brass plate on the lid marked ‘R. Napier’. The lid contains a trade label for William Gerrard, 35 South Castle Street, Liverpool, and a circular handwritten label, ‘Helen, Francis & Gordon gave this instrument to Father Christmas 1907’.

The instrument has a bronzed limb with inlaid silver scale from -2° to 134° by 5 arcminutes, measuring to 122°. The sextant has a silver vernier measuring to 5 arcseconds, with zero at the right.

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

The instrument once belonged to Robert Napier (1791-1876), a marine engineer and shipbuilder on the river Clyde, and later to his son James Robert Napier, also a noted marine engineer.