Before revision: Roy's first task (1784) was to measure a base line between Hampton Poor House () and King's Arbour () on Hounslow Heath, a distance of just over 5 miles (8 km).A full account of the measurement of the Hounslow Heath baseline is given in .
After revision: Roy's first task (1784) was to measure a baseline between Hampton Poor House () and King's Arbour () on Hounslow Heath, a distance of just over 5 miles (8 km).A full account of the measurement of the Hounslow Heath baseline is given in .