I do not often modify my unit, so I cannot speak to that. But there is no "best sensitivity". It depends on the soil you are searching. You will learn this with experience. Red Clay is nothing like beach sand. When I am in a new area I will bury a few coins and then adjust my settings as I scan over 'known' targets. Once I have those settings I go hunting. I have a 14k gold ring that I keep for luck. I often bury that and scan it as well. I've seen books that tell us to build a sand box and fill it with different targets, including junk, at different depths to learn our detectors. This is fine, if you are searching in sand. I can tell you that Alabama loam is a lot different from West Texas desert desert gravel and sand. It only takes a few minutes each trip out to tune your detector.