Both Halley's and Bradley's 8-foot (244 cm) mural quadrants are mounted on a wall of nine massive stone blocks set into the bedrock of Greenwich Hill. Halley, who had made a name for himself studying the less well known stars of the southern celestial hemisphere, originally set his quadrant on the east side of the wall, roughly in line with Flamsteed's first Greenwich meridian and facing south.

The design of Halley's quadrant provides a simple, strong and accurate instrument. Above the wall, the visitor can see remnants of the two viewing slots that were opened in the roof.