Q. What is a bench mark?

A. A bench mark usually takes the form of a horizontal line with an arrow pointing up from below. These marks were cut by Ordnance Survey levelling staff to provide a network of points at which height has been precisely measured (to the centre of the horizontal line) above sea level. There used to be about half a million bench marks in Great Britain but they are not needed any more and about half have disappeared. You can find them mainly on buildings (especially churches) and on bridges.

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