These are the unfinished remains of a 5ft wall or mural quadrant made by Flamsteed's instrument maker, Abraham Sharp. Though never used or intended for use at Greenwich this is one of the few surviving examples of the work of the Observatory's 17th-18th century instrument maker, Abraham Sharp.

A mural quadrant is, as the name would suggest, a telescope mounted on a quarter circle frame which is then mounted on a wall aligned north-south so that the two sides or radii run vertical and horizontal. The telescope is pivoted at what would be the centre of the circle while the circle's circumference carries a scale from 0 to 90 degrees. This allows the observer to measure the angular height of the star he or she is observing.

The telescope here is missing or perhaps never made. The frame is made of oak, strengthened with iron. The central radial bar was missing in 1865 and replaced at that time and the vertical oak was reduced by 2 inches in 1960 because of woodworm. The scale around the circumference of the frame is engraved on an arc of sheet brass. The inner radius of the brass is 4ft 11 inches and the outer radius is 5ft. The finished graduations are those in the band near the outer edge.