For this exercise, you make a serpentine along the length of the arena, rather than across the width. At X, perform a downward or upward transition and then continue down the remainder of the centreline, turning back in the opposite direction.
This exercise requires that you help your horse to remain straight down the centre of the arena, before and after the transition at X. This improves your eye for travelling away from the edge of the arena. It also helps your horse to improve his transitions and the bend through his body.