First couple casts off around twos, leads up the middle back to place.
Second couple casts up around ones, leads down the middle to place.
All hands halfway round. 15-16 Ones cast down while twos lead up the center to progress. The couples dance in pairs, with the couple closer to the music being the ones, and the couple farther away being the twos. The dance repeats with the twos moving up the line and the ones moving down. When you reach the end, wait out one cycle and then come in as the other couple.