I've done a lot of testing the past few months using every combination possible with every knob and switch and adjustment the GT has and I'm back to setting up my Gt the same as I've always done but I did do some additional testing for you. I did the testing the other day at the beach on deep targets using different sensitivity settings and sweep speeds and had some interesting results. I was using my standard settings with 0-disc., 0-notch, iron mask on, full volume, slight threshold and on this day sensitivity set to where I maintained a steady threshold (no nulling) with a medium sweep speed, about 2 sec. for a 5 foot sweep. This ended up being about 2:00 on the sensitivity. First target tested was a very faint repeatable high tone. I centered over the target and with a very slow sweep speed and about a 12 inch side to side sweep I started increasing the sensitivity very slowly while sweeping. I increased the sensitivity up to about 9:00 sens. slowly and then back down slowly to about 3:00 with very little if any change in the targets depth response. Switching to auto sensitivity the target disappeared completely. I marked the target and then set the sensitivity back to 9:00 and came at it again with my normal sweep speed and of course was in a null with no threshold. There was no response as I came over the target. I then came at it again several times slowing my sweep each time and was not able to get a response until I narrowed the sweep to about 12 inches or less while directly over the target. Once it locked in I was again able to get a soft repeatable signal. I then repeated the test at 11:00 and then 1:00 and again at 3:00. At 1;00 the threshold was intermittent and I could hit the target again but had to slow the sweep to get the same response as the 2:00 setting. I didn't notice much change at 3:00 but there might have been a slightly weaker response but it was close. The target turned out to be a deep dime. I repeated this test on several other deep targets with basically the same results. I also tested different volume and threshold settings using my usual beach settings above on deep targets and these were more of a surprise. I liked the response of the deep targets with the volume at 3:00 with a slightly louder threshold instead of my normal full volume and barely audible threshold and this will be the only change I make in the way I set my GT up in the future. In my ground and on the beach lower sensitivity gives me much better performance. The more sensitivity you use the more critical your sweep speed becomes to hit deeper targets and higher sensitivity seems to have less of an effect on the actual depth you can achieve at least in bad ground.