At 01:30 30/05/03 +0100, you wrote:
They are Ordnance Survey "bench marks" which are precisely surveyed for
Something the meaning of which eludes both me and a friend is an odd
sign which we have spotted on things as diverse as old buildings -
colleges, churches, and mileposts.
their height above the zero level for the contours seen on ordnance survey
maps. Their height is measured using precise methods and is accurate to
about a cetimetre.
Like the "Trigonometrical Points" that you see on the tops of many hills,
which are accurately surveyed in plan position (latitude and longitude,
and/or grid reference), they are largely being supplanted by Global
Positioning Systems (GPS) that use the same orbiting satellites as sat-nav
systems in some expensive cars - and motorhomes!
Hope this helps!
I agree with this having lived in a 10 year old cottage 30 years ago. I
remember when the ordanance survey man came around looking for the bench
mark on the cottage. Every building marked on an ordanance survey map has a
benchmark on it somewhere. This shows it is marked on the map.