not sure but circuit symbol is an inductor, one showing more inductance than the other, could be seperate chokes in the machine, not sure what the benefits are though.
Take a pic of the inside of machine including the other side of the sockets
This control can only be used on dip transfer, and it fine-tunes the arc by either making the arc hotter or cooler. To rapid a rise during short circuiting will cause globules to explode out of the arc at the current peak, thus creating excessive spatter. Too slow a current rise will cause the electrode to freeze in the weld pool. Therefore :-
Low inductance setting:- Gives higher short circuiting frequency and relatively cold welding
High inductance setting:- Gives lower short circuiting frequency and longer arcing periods between short circuiting giving hotter welding.
Inductors wont tend to change a DC current it will just present a small amount of resistance, if its AC current it will tend to limit the current flowing through it, a bit like the shunt on an A.C. arc welder transformer.
I agree the the sockets on the left affect inductance & the pinch effect on the wire, as a general rule the thicker the material the more inductance needed (experiment with token pieces to find the best for you). The middle knob is ramp up speed, the wire will feed at full speed on o and take longer to get to full speed on 10, but the higher you set it the more likely you are to experiance burn back onto the contact tip (again practice makes perfect), the knob on the lower right is spot weld time, the higher the setting the longer the wire runs for when the trigger is pressed, it should cut out after time even though the trigger is still pressed, just release the trigger to start again !