Elton, Setting the proper GB level is basically the same thing as having the detector "discriminate out" the effects of that ground. The Tracking mode is designed to "continually modify" the GB level of your detector based on changes in ground conditions under the coil. As such, a "fast recovery" detector with Auto Tracking will nullify targets that they consider to be part of the ground matrix. If you are sweeping along in an area with moderate or little trash, the X-70 will not balance out targets. But if you repeatedly wiggle the coil over the same target, the X-70 will eventually recognize that specific target as part of the soil composition and ignore it. Once you "move on" the X-70 will readjust the GB based on whatever is under the coil at any specific moment. My recommendation for those using Tracking is to turn the Tracking off when pinpointing or "Xing" over the target. This is done automatically by pressing the Pinpoint pad. (the GB level will remain at the most recent level chosen by the X-70 while Tracking. So turn it off before you "X"over the target) Once you get the target located, press the Pinpoint pad again, turning the Tracking back on, and continue your hunt.
Personally, the sites I hunt allow me to run the sensitivity at or near max. I get some falsing. But over the years, I have learned to ignore the chatters. Worst case scenerio is that I have to sweep the coil over the same spot and listen for consistency. The only time I lower my sensitivity is when I don't want the coil to be as "hot". This may reduce the depth of detection. But it allows me maximum target separation. (e.g. 6-inch coil in heavy trash.)
JMHO HH Randy