Geograph - photograph every grid square

Bench mark on top of the milestone. For a wider view of the milestone see SD4764 : Milestone near Slyne and SD4764 : Milestone near Slyne Link
A bench mark is an Ordnance Survey arrowhead sign found on walls, bridges, churches and specially erected triangulation pillars where the altitude above sea-level has been accurately measured by surveyors. The arrowhead points to a horizontal line above it which marks the exact altitude.
With rivets and pivots there is no datum (horizontal line) cut, the pointed-to horizontal surface defining the datum height.