I got a free MIG welder today! The problem is, it's an oddball make (FRO) and it didn't come with a manual. The previous owner never used it so he couldn't help me. I haven't tried it yet because I am puzzled by the front panel controls. See the picture; besides the on-off switch there are three knobs. The upper right one is obviously wire speed; I think the center left one is voltage. The one that has me puzzled is the bottom one. It clicks off at the "0" setting and moves smoothly between 1 and 10. Anyone have a clue what it does?