The pillars were located by triangulation from Ordnance Survey Control
This entailed observing at the pillars and selected OS control stations in well conditioned figures such as braced quadrilaterals or centre point polygons.
The actual observations were completed using a Tavistock 5inch Geodetic theodolite at each station. Sixteen "rounds" were observed on sixteen zeros to first order criteria. Initial checks were completed on site and the observations passed to the Survey production centre for final calculations. Due to the flat nature of the areas being surveyed the majority of stations were in elevated positions such as Church Towers, water towers or in some cases Bilby towers constructed by ourselves. Some pictures can be seen here