I would like to say at the outset, that there is only one way to guarantee you get the best out of your machine and not miss any targets. That is to hunt without any discrimination (all metal) and dig every signal. Having said that, its not really practicable unless you’re detecting in a junk free zone such as a countryside field, where signals of any kind are rare. It is my experience that you can trust your detectors ability to recognise and reject iron, so use it! It will save you a lot of unproductive digging.