IT is 70 years since the start of the Ordnance Survey's triangulation of Great Britain.

At that time it took 26 years to complete the 11,678 observations starting in Northamptonshire, finishing in Cumbria and taking in the whole of the United Kingdom.

To assist in their huge undertaking, more than 5,500 triangulation pillars were erected, and these are scattered around the country, not only on the top of hills and mountains but also hidden away in towns and cities.

In the map area of York and Selby, for instance, there are 13 "trig" pillars waiting to be re-discovered. The highest is at Garforth water tower and the lowest is near the railway at Upper Poppleton.

The Trig Tracking Society is re-enacting this survey and is looking for volunteers, young and old, to become observers. All it would mean is during the coming summer months to visit as many as you can of those triangulation pillars in your area, to observe their condition and let us know what you find.

If you would like to be part of this fascinating project please send a stamped addressed envelope to the Trig Tracking Society at the address below and we will send you a list of trig stations in your area, where they can be found and all the information you will need.

Andy Smith,

Trig Tracking Society,

Mousegill,

South Stainmore,

Kirkby Stephen,

Cumbria, CA17 4EU.

Updated: 10:20 Tuesday, April 18, 2006