Since the of Bergstrand's Geo- dimeter in 1946, and Wadley's Tellurometer in 1956, there have been numerous Electromagnetic Distance Measurement (EDM) instruments produced throughout the world by a variety of companies._x000D_
This form of measurement has not merely replaced other methods of measurement, but has caused considerable change of emphasis in survey techniques. Major control surveys are now being accomplished using trilateration instead of triangulation. The surveying of open cuts or engineering work may be done in a fraction of the time and, in the majority of cases, to a greater degree of accuracy than with older methods._x000D_
It is surprising that with this new tech- nology and development of EDM equipment which is compact, easy to use and no longer so expen- sive, no advance has been made in underground surveying. If we look at equipment being used by the majority of mining companies, we see that there have been very few changes since the Second World War. Very little research has been carried out to enable the surveyor to do his work more easily in conditions which, at the very least. are hazardous.