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A brass disc set in stone.
Also known as: Survey marker, Geodetic monument, Survey disc
The permanent marker set into the ground recording a surveyed position.
Records a surveyed position permanently in the ground.
Contexts: Navigation, Maps
Placed for a reader who does not yet exist: the disc is set so that a surveyor decades later can reoccupy exactly the same point, which is the only way measurements separated by years can be compared.
Contexts: Navigation, Maps
The punched centre is the datum and the lettering is not, so a disc read by its edge rather than its punch mark gives a position wrong by centimetres.
Contexts: Navigation, Maps
A metal disc set flush into rock or concrete, stamped with an identifier, the agency's name, a year and a punched centre point.