The sextant consists of circular brown-lacquered brass plates and a lid with a bayonet fitting that when attached to the back of the instrument serves as the handle. The lid has a brass handle, and contains a paper table for natural tangents to the power of 100. The index arm is moved by a milled knob on the upper plate. The sextant has two index shades, in red and green, which are moved by levers. The index glass is non-adjustable and the horizon glass is moved by a milled key shipped in the upper plate.

Attached to the sextant is a single lens magnifier on a 45mm swivelling arm. There is also a sliding sight vane with one pinhole and a blue shade.

The instrument has an inlaid silver scale from -5° to 130° by 30 arcminutes, measuring to 115° (the digits are read from the pivot). The sextant has a silver vernier measuring to 1 arcminutes, with zero at the left.

The sextant is contained in a fitted leather carrying case with a strap, and lined with red velvet. The case is marked, ‘D. Mason and Sons, Ltd. Birmingham 1918’.