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Painted or fixed points recording position underground.
Also known as: Underground survey station, Mine plan datum
Underground survey marks are fixed points from which a mine's workings are measured, since satellite positioning does not reach below ground. Abandoned mine plans, tied to these marks, are the primary evidence for what lies beneath a site being redeveloped.
Fix survey points underground from which workings are measured, since satellite positioning is unavailable below ground.
Contexts: Technical drawing, Maps
Tie abandoned mine plans to the surface, which makes those plans the primary evidence for what lies beneath a redevelopment site.
Contexts: Technical drawing, Maps
A painted cross or a fixed metal plug in a roof or wall, carrying a stamped reference number.