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
Three instruction text books for surveyors, 1950-1959,, issued by the British Ordnance Survey ( The "Red", "Blue" and "Biscuit" books) Surveyor's instruction text books, British, 1950-1959