One large bar for Colby's Compensation bar, as used on the Lough Foyle Base, 1827-1828. These are 10 feet in length but will change with temperature change. A bar for Colby's compensation bars
Original photogrammetric plotting machine designed by Prof. E.H. Thompson, made by Hilger and Watts, 1953-1954 Original photogrammetric plotting machine designed by Prof. E.H. Thompson