The MXT is an excellent, very versatile detector. As you use it, you will learn that multiple targets close to each cause some of the bouncing confusing display. The smaller coil will help that problem a great deal. For really trashy areas, even smaller coils are good. Listen for good, clear, repeatable tones that are repeatable in every direction. The trash signals usually are scratchy, or crackle and pop and are not repeatable in all directions. However, you should eventually get a seat of the pants feeling for sounds that just are a bit different enough to make you wonder. Often it turns out those can be a target worth digging. At first, it will be WORTH YOUR TROUBLE TO DIG EVERYTHING in order to get a handle on just what the sounds and display are trying to tell you. I highly recommend learning to go with the sound first, display second as the display is a machine's best guess, emphasis on guess. In my own experience I've found the MXT to be very accurate down to 6 or 7 inches on coins and sometimes deeper. If the target is actually a coin it will ID as a coin. For a fair bit of trash however, the opposite is true. The trash target may often show up as a coin, and jewelry items may read or act as trash.
I've seen it mentioned that it takes 100 hours with a machine to really get to know it. I feel that is pretty true of the FIRST machine a person uses. After that, one can carry the experience over to the next machine etc. Your best bet for getting the most out of your MXT is to get out and hunt, hunt, hunt, digging pretty much everything and paying attention to the different responses on the different targets. Use your 5.3 coil in trashy areas and if you aren't already, wear decent headphones.
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