Warm-up drill. The blue guys are actuall just discs. Disc #2 goes back and forth between the NE and NW corners, and the other discs basically stay on their respective corners. I showed it through a full cycle and a bit. It basically repeats from there.
Focus on the mark (R1, how R4 is out of position later). A demonstration of why holding the force is so important in a stretched field situation. Also a demonstration of how to cut deep, from the side opposite the disc is moving to.