Benchmarks in Stratford sub Castle
There are about half a million benchmarks cut by the Ordnance Survey for surveying from 1831 to 1993. From 1921 these were known as Ordnance Datum Newlyn points as sea level was taken as a mean at Newlyn, Cornwall. A brass bolt there marks the mean tide level of levels taken every 15 mins from 1915 to 1921.
The horizontal line chiselled out at the top is for an angle iron (L shaped and usually a 90° angle) to be placed in it. This gave a platform (a bench) for a levelling rod to be positioned by surveyors. Beneath it is a heraldic broad arrow with a tang between two barbs. It has been used since the 14th Century to denote Royal, Government, Board of Ordnance, Ordnance Survey (as here) and Military (including Navy perhaps as an anchor icon) and MoD use over the centuries. From the 1830’s it appeared on prisoners’ uniforms and still does in any cartoon denoting convicts. In 1875 it became illegal to copy it without authority.
When they were last verified in 1958, the village had six such marks. Three have been lost since then from Stratford Bridge, Mill Lane Avonside Bridge and Old Sarum. Three remain, on St Lawrence Church 51.185 m, outside the Parsonage 50.493 m and on the (back of the) Parliament Stone 61.807 m above (mean Newlyn) sea level. However the Newlyn sea level itself is rising at 1.8 mm a year. These marks are redundant now in this GPS age and disappearing with time, only that on the church here is well preserved.
Article and Images - Kerry O'Connor
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You may also be interested to read about a benchmark on the rim of a cannon buried in a field to the east of Old Sarum, mentioned in another article Mudge Mapping Monument