Industrial Archaeology Hiding in Plain Sight - Ordnance Survey Trig Points

Surrey History Meetup is running a series of Lockdown Lectures for you to attend from your own home via the Zoom web conferencing system.

This first talk is about the Ordnance Survey's trig points.

The Ordnance Survey have been mapping the UK for over 200 years. Until recently they used simple mathematics, theodolites and a national network of benchmarks and trig points to achieve one metre accuracy, a triumph of engineering in its day. That technology has now been replaced by more accurate satellite navigation and the physical position markers are redundant.

The best known of these markers are the trig pillars, a common sight when walking in the country. These were built to last but they are decaying slowly. Other markers such as bolts and surface blocks are more easily damaged. The village of Bookham was served by three surface blocks, all now vanished, possibly just buried a few centimetres below the ground, or maybe dug up and destroyed.

The speaker Simon Ritchie is a Surrey-based software engineer interested in history and archaeology. The talk arises from work he has been doing on measuring the accuracy of satellite navigation systems. the talk was originally to be given to the Leatherhead History Society, but that event had to be cancelled.

Simon has put some background notes on his website, including links to the other websites that he will be mentioning during the talk - https://goblimey.com/courses/trig.points.pdf.

To see the link and to get the password to join this talk on Zoom you need to join this meetup, which is free. The password will be sent out before the meeting, so don't wait until then to join. Press the "Attend online" button below and the meetup system will take you through the procedure. Once you have joined you will also get notifications about all our other events.

To view the talk you will also need to download the Zoom software, which is available for Windows PCs, Macs, Apple phones and Android devices from https://zoom.us/download. You should also visit the test conference to make sure that everything is working: https://zoom.us/test. On the day, you may care to join our conference ten minutes or so early to sort out any last-minute problems.

Web conferencing systems like Zoom are very prone to problems due to flaky WiFi connections. Using a wired connection is always better, but if you can't do that you should try and place your computer close to your broadband modem.

There is no charge for the Lockdown Lectures but we would appreciate a donation to Dorking Museum or Age Concern Mole Valley, or the equivalent for your area.