[Elecraft] Newbie question... AGAIN!

[Emory Schley]

OK, I'll try this again...
 
I'm the new owner of a KX2 and am trying to learn all I can about the rig. One thing about it truly stumps me. The multi-purpose knob at the far right side of the rig is labeled OFS, and for the life of me, I cannot figure out what OFS stands for. I turned my computer loose on the PDF copy of the Owner's Manual and could find nothing identifying that label there. I also searched through the printed version of the manual. If it's in there somewhere, I've been unable to find it. I even wrote a note to Elecraft about it, and for some reason, they ignored my note even though they were quite responsive in answering questions BEFORE I bought the radio. So, I now turn to you. Does ANYONE know what "OFS" stands for?
 
Thanks, Emory N4LP