The sextant has a polished brass frame and a wooden handle. The tangent screw, which is bent, is located on the front of the index arm and the clamping screw is on the back. The lower part of the index glass is silvered, and can be covered by the Maskelyne flap, whereas the upper part is not silvered. The sextant has three shades, two red and one green, and one red horizon shade. Index-glass adjustment is made by a screw and on the horizon-glass by screws, a Dollond’s extended lever and a clamp operated from beneath the telescope bracket. Attached to the sextant is a threaded telescope bracket in two parts, fitted for correcting collimation error. It has perpendicular adjustment by a rising-piece and a milled knob. The telescope is 129 mm in length with an erect image and two parallel cross wires. The sextant has no box.

The instrument has a bronzed scale from -3° to 139° by 20 arcseconds, measuring to 124°. The sextant’s vernier measures to 30 arcseconds, with zero at the right.

Admiral Sir John Thomas Duckworth (1748-1817), the original owner, defeated a French squadron off San Domingo in 1806 and commanded an expedition against Constantinople in 1807. On the index arm his year of death is erroneously marked 1819.

Peter Dollond patented the horizon glass adjustment (no. 1017 of 1772); the scale mark indicates that it was divided on Ramsden’s engine.