I would have to entirely agree with James. If you're not digging the minus numbers, you could be missing out on coins or relics. But I also feel it depends on the tones you're listening to , and the type of ground you're detecting in. I'm not very technical, but I'll explain as best I can from my personal experience: At one particular beach here in Aussieland, I've been pulling out the old one and two cent pieces, no longer in use. They've been in this very course orange sand for years, and being copper, tend to erode and get the typical green coating on them. These coins, out of dirt would read around 35 or 37. From this sand, they're jumping from -3 to +6, occasionally the coin with this reading will change to a fluctuating +35 or +37, if I slow the coil over the target very slowly, and then hold the coil directly over it momentarily, the signal is bouncy, but you can tell it's something worth digging. But one hour of digging landed me around 30 of these coins. On the gold fields, I've had much older coins read at -2 or -3, and other relics at -6 or -7. The type of signal you're getting with the reading is also very important, but it takes practice to realise a potentially good target. Simply, dig everything, then you'll learn what to go by. Hope I've helped somehow.
Cheers Angela
