This is how you do it:

“Set up the exercise with a jump at the centerline (a vertical with two poles, with a ground pole before and after), and a cavaletti 12 meters before and after the jump. Frame the center jump with poles on the sides. 

Ride the exercise at a canter, with three strides between the jump and the cavalettis. After the second cavaletti, you can go either left or right and then repeat the process. 

Start by placing the center jump at 60 cm. Try out the exercise and get a feel for it with both canter leads. The first part of the series might feel longer than the second, so try to maintain a working canter with a normal distance to the first cavaletti. Sit back in the saddle after the center jump and work in the three strides with a normal distance to the second cavaletti.

If your horse is feeling good and strong after the series, then transition to a trot. Once you've found your rhythm, come back to a canter and continue the exercise.” 

Make the exercise easier: Use the cavaletti poles as ground poles instead.

Make it more challenging: Raise the center jump.

Download the exercise here.