I was going to get an SDC however I haven't found in my price range as yet. I did see a GPX 4500 for sale at a very good price. The ad says its all good and ready to go. I was just wondering how do you test a used metal detector? I did a bit of search here and couldn't really find anything related, did a you tube search and found a video from the Miners Den and the fellow went through testing a 5000. Basically all he did was factory reset and do a couple of ground balances, is this all that's required?