Division within OS1813-2008Records of the Directorate of Field Survey and predecessors
Records of the Field Directorate (formerly the Trigonometrical and Levelling divisions) relating to triangulation and survey work.
Old Triangulation records are in OS 2 and OS 17, County Series parish acreage lists in OS 4, magnetic surveys in OS 6, branch files in OS 13, papers in OS 15, records of the Second Geodetic Levelling in OS 16, Cambridge Radio Telescope observations in OS 18. Original name books are in OS 34. 25-inch scale object name books are in OS 35 and one-inch scale name books (Seventh Series) are in OS 50. National grid object name books are in OS 67. Triangulation Stations files are in OS 69.
A number of series of technical records are still held by Ordnance Survey: OS 19, OS 20, OS 21, and OS 22.