As far as I know ground tracking is just another term for ground balancing or how your detector is set up to handle any mineralization found in the soil you are detecting in. If your detector is not properly ground balanced, higher levels of minerals in the ground will rob you of the depth you'll need to find deeper coins such as old silver. There are three basic kinds of ground balancing, (fixed) which is preset at the factory, (manual) in which the operator has to do it himself and (auto) or (tracking) such as what you are probably talking about, where the detector automatically tracks the amount of mineralization in the ground and then adjusts itself to best handle any varying amounts of mineralization, so as to give you the most optimal performance at all times. One thing that can throw your "auto or ground tracking" OFF and thereby cost you depth is by repeatedily sweeping over a target, as your detector will begin locking in on the stronger signal from the metals in the target rather than the weaker signals from the minerals in the ground.
