It is actually a simple manuever. Just visualize 4 points for every quarter. Feed your rudder and elevator as you would for a slow roll. You can do as many points as you can possibly see. 32 is the most that I have done with good symmetry. I also do what I call a stutter roll, perhaps it has forty or fifty points, but they are not symmetrical on the points. Digital servos and a well tuned airplane help lots here.

Mark