The reflecting half-circle has a brown and yellow-lacquered brass frame, with a wooden handle. The tangent screw, working against a spring, and the clamping screw are at the bottom of the index arm. The instrument has four half coloured shades, two red and two green. The index glass and horizon prism are non-adjustable.

Attached to the half-circle is a magnifier on a 135mm swivelling arm with a frosted glass shade. 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 162 mm in length with an inverted image. An extra drawtube is 86 mm long with an erect image. Another extra drawtube is 94 mm long. Accompanying the instrument is a rotating shaded eyepiece with three shades, one green and two red, and a prismatic eyepiece for observing through the telescope at a right angle to the frame.

The instrument has a polished brass limb with an inlaid silver scale indicated from -10° to 140°, and from 105° to 180°, although the entire scale is divided by 10 arcminutes, measuring to 180°. The reflecting half-circle has a silver vernier measuring to 10 arcseconds, with zero at the right.

The reflecting half-circle are contained in a fitted rectangular polished mahogany box, with a Kew Observatory certificate of examination in the lid, dated December 1898.

Two prisms replace the horizon glass; one is for forward sights up to 120° and the other for back-observations extending the instrument’s range to 180°.