Until fairly recently, none of my bikes had barrel adjusters on the downtube. One has levers and the other two just had stops with inline adijusted in the housing near the shifters. Now I have a bike with dt barrel adjusters, but rather than right side being standard barrel, its wing type lever.
I didn't give it much thought when I got them since I ususally just use the adjuster on the rear derailleur to make any adjutsments; I am not even sure where I got them (maybe the came with the frame) since they generally cost more, and I don't recall paying extra for them as compared to regular adjusters. Since I have had the bike, the wing has been set all the open (so I would have only be able to increase cable tension if need be)
So as I was fine tuning my RD after a recent install (see franken derailleur thread), it occurred to me that perhaps there is a "right way" to set the wing-- either "right" in the sense that it should be set 1/2 way to allow either increasing or decreasing tension or "right" in the sense that "its just the way it done"; sort of like how one's rim labels are supposed to face in the same direction (see very long thread on that issue not long ago).
So, since these adjusters aren't strictly necessary for RD adjustment, how do folks set them?