I apologize if i am hogging the forum, I was reading that book and the guy was explaning how you can tell the diffrence in all metal on a good target and one that is not so I took a aluminum bottle cap , and a silver quarter, and a steel bottle cap all about the same size put the GT in all metal and swept all targets , and guess what you can clearly tell the diffrence from the silver and the other two on the silver the signal will drop off sharply after the sweep and on the aluminum it has a longer drawdown and a bit of a more raspy tone the beer bottle top also has the longer sound as you pass the cap it fads slower and has a lower sound the guy in the book used this to find many a gold ring and silver coin you can clearly tell and this is in all metal and what he said is this is possible because of the multi frequincy Intresting