I like the Motorcycle example Tony.
However, there are people who could tell you if it was a Harley or other in total darkness, just by sound. It took them a lot of listening and verifying to learn, but now they're very accurate.
The same thing applies to your machine. At first, you will dig a lot of nails and other crap that you thought sounded good. Hopefully you'll start to remember what each of them sounded like. Then, you'll dig something that sounded good that actually *is* good. Hopefully that will stick in your mind as well. Eventually, you'll be able to scan a suspect target from all different directions and decide if it's worth digging or not, based on the sounds you've heard a million times before. I, too, dug a lot of nails before I started to hear the subtle differences in them, and learned the way they pinpointed off center typically. Keep in mind though, that you can't always dismiss an iffy response as bad, and you will still dig quite a few crap targets. Sometimes, those crap targets will turn out to be a nice coin hiding in the nails.
Hang in there. Make subtle changes to your machine once in a while and see if you like it better or worse. I've found Audio1 to work best for me. I also like to hunt in wide open IM -16. If you're discriminating any at all, you will find that once in a while the cursor (or digital numbers) bounces up into what you think is good. If you're wide open, you will find that the cursor typically locks on to a nail accurately, with occasional jumps to the high right silver area. Keep at it. Eventually, you'll be able to pick out the Harleys! If you find a buried HD, I got dibs on it! <img src="/metal/html/biggrin.gif" border=0 width=15 height=15 alt="

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HH - Rhoderman