Its expensive and pretty sophisticated. Unit has LCD dispaly, dual ground balance, etc.s Here is an exerpt from the Lorenz website:
"The Pulse GBS (Pulse Ground Balancing System) is suitable for searching at depth and specially designed electronics cancel out signals from the ground. The LORENZ DEEPMAX X3 is therefore a reliable tool to locate metal objects even with extreme soil and environmental conditions. A new improved circuit design suppresses a range of interference from power lines or radio transmitters and a power pulse technique produces very accurate signals to obtain considerable detection depths.
The LORENZ DEEPMAX X3 works with two different ground cancel filters. It has an extended depth capability for non ferrous metal objects and it is capable of identifying metal objects employing the two different target identifications.
The Pulse Ground Balancing System GBS performs well because of the time delay between the transmitting and receiving phase. The high transmitting power is a fundamental advantage and makes operation with very large search coils possible. Because of its active working principle a high sensitivity range for both ferrous- and non- ferrous metal objects is achieved."
http://www.lorenzmetaldetectors.co.uk/products/deepmax/index.php
"The Pulse GBS (Pulse Ground Balancing System) is suitable for searching at depth and specially designed electronics cancel out signals from the ground. The LORENZ DEEPMAX X3 is therefore a reliable tool to locate metal objects even with extreme soil and environmental conditions. A new improved circuit design suppresses a range of interference from power lines or radio transmitters and a power pulse technique produces very accurate signals to obtain considerable detection depths.
The LORENZ DEEPMAX X3 works with two different ground cancel filters. It has an extended depth capability for non ferrous metal objects and it is capable of identifying metal objects employing the two different target identifications.
The Pulse Ground Balancing System GBS performs well because of the time delay between the transmitting and receiving phase. The high transmitting power is a fundamental advantage and makes operation with very large search coils possible. Because of its active working principle a high sensitivity range for both ferrous- and non- ferrous metal objects is achieved."
http://www.lorenzmetaldetectors.co.uk/products/deepmax/index.php