Remember: that machine is a "motion" machine (albeit fairly slow motion). So don't make the mistake of stopping on top of the target. Got to keep the coil in motion/swinging.
Try propping the machine up on a wooden table, coil extended out far away from any nails, metal etc... Take all rings, watches, etc.... off . Set up the machine for a threshold of how you intend your hunt settings to be. Then take a variety of test targets. Eg.: penny, dime, quarter, nickel, tab, foil glob, nail, nut, bolt, etc... Wave them in front of the coil. Try various speeds, even down to a crawl or stop. Then you'll know the approx. sounds you should be getting in the ground at those depths (assuming not masked or next to some other object).
As as far as burying an object in a test garden: Make sure there's no other metals in the ground there. Don't assume your yard is "clean" Maybe go WAY out into a virgin field (where there's never been any structures, and limited to zero human activity). Try the test there. Also try the coin right on top of the ground first, before trying the same test with it buried.
