We start by hearing how the UK's network of 200 fundamental benchmarks all stem from a single 'mother' benchmark at Newlyn in Cornwall. We show how the network expanded and we learn why now, in this highly technical modern age, the humble benchmarks' days are over.

Aided by a short graphic sequence, the Ordnance Survey's Mark Greaves describes how satellite technology uses triangulation to work out the X,Y and Z coordinates of a receiver station on earth.

Surveyors have two ways of accessing and processing raw GPS data needed: via the OS-operated network of base station (the OS Net) or via self-created base stations. We look at the pros and cons of each.