mohammedreza, what's "iron stone" ?
But as for your assertion that your 2-box gemini 3 won't detect a soda can at 60 cm: Well, 60 cm is about 2 ft. Technically you *should* have been able to get that soda can with a 2-box at 2 ft. At least the TM808 is capable of that, so I'm not sure why your gemini 3 doesn't, unless you've got it set up wrong, aren't using it right, etc.... But let me tell you: "2 ft. (60cm) on a soda can is about the outside range for an object that size using a 2-box. Now if it were tool-box sized item (toaster sized or whatever), then yes, you can go to 3 and 4 ft. (1 or more meters). And if it's refrigerator sized, you can go to 2 and even 3 meters (6 to 10 ft). But no, you will NOT find a machine that can get your supposed 30x30 cm (~1 ft square tool box sized object) at 6 to 10 ft. deep. MAYBE, at best, at 6 ft. deep (~2 meters) if you've got it very finely tuned, and are listening very intently. But no, not to 3 meters deep.
Why is this so hard for you to accept? And did you ever read the "buried gold coins" thread on the general discussion page? There I addressed this whole notion of such "super deeply buried treasures". You have yet to explain to anyone here who's asked: Why do you think this is of necessity that deep? Can't you conceive of how many this is a wild goose chase urban legend that simply doesn't exist? And I've asked you several times what country your'e from, and you fail to answer that too. Phillipines I'm guessing right? Or Mexico? Countries like those (3rd world cultures) are steeped in superstitions that "treasures are everywhere, in every cave, etc...". And naturally, it's never that they aren't there. They're always simply too deep, right?

But alas, we/I are probably not going to get you to see and realize this. The human mind wants seeeooo hard to find treasure, that any counter-comments to try to cause someone to slow down and think of the reasons it's just supersition, lore, legend, will be met with disbelief. Why? Because no one wants to be "left out". So we subconsciously tend to dismiss anything that explains away the sure-fire treasure story, and it utterly must be there, "if only I had a detector that went 10 ft. deep".