The sextant has an anodized brass diamond-pattern frame with a wooden handle. The upper tangent screw and the clamping screw are on the front of the upper index arm and the lower tangent screw and clamping screw are on the back of the lower index arm. The sextant has two index glasses and one large horizon glass. It has four shades, three red, one green, and three horizon shades, two red and one green. Index-glass adjustment is made by a thumbscrew and a capstan screw and on the horizon-glass by a capstan screw.

Attached to the sextant are two single lens magnifiers. The upper magnifier is on an 83mm swivelling arm and the lower magnifier travels on a bar. 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 102 mm in length with an erect image. A second telescope is 67 mm with an erect image. It has a rotating shaded eyepiece with three shades, two in green and one in red.

The instrument has a polished brass limb with two parallel inlaid silver scales, the lower runs from the left from -5° to 160° by 20 arcminutes, measuring to 132°, and the upper runs from the right from -10° to 160° in 20 arcminutes, measuring to 126°. The sextant has two silver verniers measuring to 20 arcseconds, with zeros at the left on the lower, and at the right on the upper.

The sextant is contained in a square fitted wooden box, with a trade label in the lid for William Gerrard, Liverpool, and a circular handwritten label, ‘A/e 1907’.

The double sounding sextant was invented by Rear-Admiral Frederick William Beechey (1796-1856) about 1840 for use in surveying, where angles of three objects at once may be required (compare NAV1122). Beechey used this example in his surveys of the Irish Sea in the early 1840s. See M Barford 'D.176: Sextants, Numbers and the Hydrographic Office of the Admiralty' History of Science (2017) 55(4), 431–456.