Chris... I have a wide variety of silver specimens that illustrate structure exerts a very real impact on PI GB scale positioning. Despite the elevated gold weight, I think it is the structure that positions the 12 gram specimen on low conductive side of the GB tonal break.... hence a high-low tone response. One apparent result compared to my GBPI units is a dramatic shift in the GB tonal breakpoint to a very low conductive placement on the GB scale… a foil to low nickel GB position seems indicated from the forum examples reported to date. Based on those reports, forum readers should realize that it is not possible to differentiate any ferrous from non-ferrous based specifically on signal tones, but thanks to the information above from you and Steve, readers can understand why that is the case. Jim.