the one that slides goes down to the treadle cords, that is your adjustment for leveling the harnesses. The short end goes to the harness closest to the treadle cords and the long end farthest. Push the sliding clamp up so that you can manipulate the cable to level the harness, then push the clamp back down to keep it in position.
Sorry, no. I sold that loom last week. I have a 19" Dorset-type loom, a 26" Dorset and a small nonfolding 20" 4 shaft counterbalance loom available at this time.