If you discriminate a block large enough to eliminate all pulltabs, you will also loose anything else that reads the same (rings included).
You supposedly can dig a pulltab, determine that there are a lot of them that are the same, and then "learn" and discriminate just that type of pulltab. Unfortunately, the tabs can be in the ground at all kind of angles, depth, and in relationship to other targets that will render a narrow band of discrimination nearly worthless. It looks good on paper, though <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="
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Bottomline is pretty simple - there still isn't a detector out there that can do what you want in an operational environment.
I also must add, while extolling the virtures of the Explorer, that pulltabs do exhibit some characteristics that can make them easy for the detectorist to discriminate. They tend to bounce, are overly loud for their depth, and do not sound very smooth/round. This isn't the case all of the time, but happens enough to make me happy.
I would also recommend looking closely at the Periscope. The probe can flex pulltabs and punches through foil, so it has the ability/potential to keep you from digging up trash. It still takes time to probe a target, but it is an insignifigant time loss compared to actually digging every target that might be a ring.
Tim
