Flaunt away :-)
What you have discovered is the trim pot for adjusting the gain of the preamp. Depending on the instrument, there may be one or two, and we recently learned that sometimes when there are two, one of them has a piece of tape over it - a long story you can discover elsewhere.
You'll find lots of discussion by searching for either trim pot or gain adjustment, but the short answer is that it allows you to adjust the output level. You can rotate it through about 3/4 of a turn or a little more (it is NOT a screw) from low to high, and the difference should be quite obvious. There is no standard or correct setting, it's just a matter of what works for you (try the search for various considerations).
Seems like we should have something on this in the FAQ. I did a quick skim of topics, and nothing jumped out at me - maybe it could be called blue square with white circle, since that seems to come up fairly often?
-Bob
