Bench marks are points in the real world where the latitude and longitude (and usually the elevation) are recorded to a very, very high accuracy and precision. In the real world, these are marked by small brass discs set in concrete (or bedrock) that include certain information on them. Bench marks are necessary for accurate surveying by providing well-established starting points for measures and triangulation. bench mark database types of bench marks
Does anyone know where this one is?
FB Rock outcrop NW face of living rock, SE side of Hoylake Road
Grid ref SJ28569027
Are the bm on this map bench marks?