The sextant consists of circular polished brass plates with a lid that when fitted on the back of the instrument serves as the handle. The index arm is moved by a milled knob on the upper plate of the instrument. It has one red index shade, which is moved by a lever, and no horizon shades. The index and horizon glasses do not adjust. Attached to the sextant is a magnifier, with a single lens, on a hinged 36mm swivelling arm that has been bent. There is also an eyepiece shutter with the choice of a plain pinhole or a red shade.

The instrument has an inlaid silver scale from -7° to 139° by 30 arcminutes, measuring to 100° (the digits are read from the pivot). The sextant has a silver vernier which reads to 1 arcminute, with zero at the left.

Sir William Gell (1777-1836), the original owner, was a classical archaeologist and traveller