Bottom line, you can't really tell the difference between them. It may be possible if the pull tab is mangled that you will get a distorted edge to the tone (might also show up on the X-Y screen), this is also true of mangled can slaw. Coins and rings tend to give a purer, fuller tone, but it is very subtle. Understanding Tonal quality vice visual TID is the key to Deus. The x-y screen can sometimes help, but as you saw, on a "pristine" pull tab, it is really not possible to tell the difference.
Basically, you are just playing the odds. It's a pure numbers game. There are more pull tabs than nickels and more nickels than gold jewelry out there in the US. It is really site dependent, but a rule of thumb is 75% - 80% will be pull tabs, 15 -25 % nickels, 1 to 5% some type of gold. So play the odds at your peril or suck it up and dig 'em all to be sure. Just set your expectations, accordingly. I figure it's just always going to be aluminum, so when it is a pull tab, shrug and move on. But just when you least expect it - jackpot!
Just the nature of the biz. Some sort of cruel joke by the detecting gods that aluminum and gold will have similar TIDs. There is no real magic bullet on this.
Some detectors, like Equinox, have more stable TIDs which can help - nickels usuually lock in at 13 whereas pull tabs will fall at 14 or 12, but corrosion in the nickel can change the TID and gold depending on size, shape, and purity, can fall anywhere in that rannge. The Deus has more numbers but tends to be less stable or repeatable on visual TID in the field. Plus factors such as target corrosion, soil conditions and nearby targets such as iron can pull TIDs down. Using disc on on the Deus helps to mitigate iron-non-ferrous TID down averaging and Deus disc doesn't affect depth like it does on other detectors as long as you keep it 15 or less (I like to keep it between 7 and 10).
Anyway. HTH.
