Before revision: The Principal Triangulation of Britain was the first high-precision triangulation survey of the whole of Great Britain (including Ireland) , carried out between 1791 and 1853 under the auspices of the Board of Ordnance.
After revision: The Principal Triangulation of Britain was the first high-precision triangulation survey of the whole of Great Britain and Ireland , carried out between 1791 and 1853 under the auspices of the Board of Ordnance.