This instrument was used for both astronomical and navigational observations. In astronomy, it could measure the altitude of the stars, and in navigation, it could determine latitude and calculate the time.
It consists of a frame with 8 columns supported on 4 thick strips. On this framework there is a semicircular metal plate and 2 serrated circles that allow the quadrant to move. It has 2 ranges, one in the quarter circle and the other in the base of the support axis.
The quadrant arc has the inscription "J. Bird, London." John Bird (1709–76) was an astronomer and astronomical-instrument maker. He created impressive instruments for the observatories in Paris, Greenwich, Oxford (Radcliffe Observatory), and Cádiz.