Homebrew, I see Andy has already posted a response, but I'd like to give it a shot, from a little different perspective.....
1. Is the Target ID Stabilizer similar to the Average function of the White's XLT?
To directly answer your question, no, the X-70's Target ID Stabilizer is different technology than Whites Averaging function. But, both "tools" provide processed target ID information for the user, allowing a better understanding of what is under the coil. With Whites, it is target averaging. With the X-Terra 70, it is Target ID Stability. Whites XLT does it by averaging a group of readings, in an effort to give the user an "educated guess" at what is buried. The X-70 allows you to activate TID Stability in highly mineralized soil conditions, to provide the user an "educated guess" at what is buried. So, although they offer two completely different technologies and provide totally different information, from the perspective of providing the user a better idea of what it is he/she is looking at on the VDI, they both do. I guess you could consider that being similar?? I don't like to get too hung up on technicalities. 7-Up and Coca-Cola are different. But at a given time, either one will quench my thirst.
2. With the target ID stabilizer OFF, I assume the X-70 would probably vary no more that three notches on a U.S. coin?
Maybe Andy isn't familiar with the article I posted to understand what you are referring to. But, I think we all know that target size, depth, ground conditions and outside interference have an effect on TID. Regardless, many of us who have used the X-Terra 50 know that consistency is the key. As pointed out in the article, if a specific target is detected, and you follow the procedure I outlined, you can get a pretty good idea if that target is a US coin or not. To answer your questions about the X-70 being similar to the X-50.... yes, early indicators look like it will be similar. Although I have not found many coins (so far)that vary at all, some have varied by one notch in one direction or the other. Note that there has been a post stating that they have found coins that have varied by two notches. But, as you indicated, the "width" of three notches on the X-70 is the same as two nothces on the X-50. I am still in the process of compiling my field test results and hope to have them completed soon. Part of my report will include more detail on target ID, similar to that I posted on the X-30 and X-50.
3. With the target ID stabilizer ON, would the variance narrow to two notches?
I haven't found where the Target ID Stability has made any change in the number of notches that a specific target varies. But keep in mind that I haven't found any coins that varied more than one notch, yet. If TID Stability does narrow that gap, I would suspect the variance is a direct result of mineralization. If the manual's reference to "highly mineralized soil" has relevance, living in an area with moderate soil mineralization might not allow me to make more specific determinations. But, as I said, my tests are still underway. And, I will keep you all posted. Thanks.
HH Randy