Welcome to the forum, sensitivity can also be though of in terms of depth, The lowest setting will limit the depth somewhat but will also make things you discriminate out less likely to chirp, sort of stabilizes it and also if there is interference from power lines or other sources it help calm down the chatter.
all detectors are different but I only lose about 1/2-3/4 inch on the lowest setting with my Tesoro and usually run mid way up at 5-6 and have great depth an stability, if your getting too much chatter (false signals) then back it down, nothing wrong with starting at the lowest setting and raising it up till it affects the operation. If your in a cleaner area an it can handle the full up position then by all means turn it up.
A good target will give a good signal always unless it is at the fringe of your detectors depth capability or is an unusual shape like a broken ring or chain, then it can be inconsistent and choppy sounding, these can be identified a little by your depth meter, if it shows 7-8 inches then it could be a deep good target but if it is choppy signal at 3 inches it is probably a target you discriminated out and is just getting past the setting due to an unusual shape or mixed metals.
Best approach to begin is dig all the good solid signals, you can always go back and dig the iffy ones later as you get better with the machine.
Good luck out there.
