OS 561840-1968Ordnance Survey: Trigonometrical and Levelling Divisions: Levelling Heighter Lists
Records from the Primary, Second and Third Order Geodetic levelling of Great Britain by the Ordnance Survey 1840-1968.
The lists contain descriptions and heights of all bench marks, given in levelling line order and to 3 or 4 decimal places. The series also includes detail pamphlets, created in the field and recording extra bench marks not included in the abstracts nor in the modern electronic database currently in use at the Ordnance Survey.