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This thread reminds me of when TID first came out, on the very first detectors, in about 1982/83-ish: The dealer came to our club meeting, and set it up on the table for a demonstration. He showed how a gold ring he'd brought read one way. Then he waved a pulltab, and it gave yet a DIFFERENT signal. Foil gave yet a 3rd signal, and nickels yet a 4th signal. Wohoo! Imagine our excitement as we all thought it was finally possible to pass various tabs and aluminum, yet dig gold (provided you dug the *right* tones and TID #s). Several guys in the room ran out and bought that early primitive Teknetics, thinking they were going to dig gold rings till their arms fell off

Imagine their surprise, when they discovered that an AWEFULL lot of tabs sound exactly like gold ring, and an aweful lot of gold rings, sound exactly like tabs. Doh!
You see, yes, some gold rings "sound different" (TID, etc..) than certain tabs. Sure. But so too does each tab sound different than the next. And so too does each gold ring sound different from another gold ring. Aluminum and alloyed gold share the same conductivity, on a size-per-size basis. So to show a *particular* gold ring sounds or reads different than a *particular* tab, doesn't mean much, unfortunately.
About the best you can do is play the odds (ring enhancement programs), to avoid certain common recurring junk items (like the certain style/size round tab that recurringly hits in the same TID range). But you can throw such programs out the window, the minute you get into a place where lawn mowers have sliced up tabs and cans. Or places where tabs come in all different sizes and types (there were many different tab weights/sizes over the years). Or places where the beavers tails come disattached, etc...