First day cover - Tellurometer

This is an official first day cover of the stamp that was issued in Pretoria, Spith Africa on the 12 February 1979 commemorating the invention and development of the Tellurometer by Dr Trevor L. Wadley.
The Tellurometer was developed by Dr Wadley while working at the CSIR in 1954 and went into production in 1957. Capable of measuring better than 1 part in 100'000 over distances of 50 km (30 miles) in the early days. The later models were capable of measuring fully automatically after they were set up at the end points in just 10 seconds. During the 50's and beyond this was one on the great leaps in geodetic surveying allowing for much higher speeds in setting up national grids. Since then it has been superceeded in many respects by carrier phase capable survey GPS units that can measure to similar accuracies over similar distances. The early tellurometers made use of the microwave link to provide a intercom speech link that greatly assisted in setting up in the days of very poor communications infrastructure.
I know of a place that had a few of the early Tellurometers for sale around June 2007 and they may still be there. They also had a few obscure Survey GPS units that are not mentioned on the net and some obsolete LASER ranging devices. If you are interested in such things send me an email and I will try and find out if they are still available.