How can a rider determine if they are on the correct diagonal while riding?

To determine if a rider is on the correct diagonal while riding, observing the movement of the horse's front outside shoulder or leg provides a clear indication. When the horse moves in a particular diagonal pattern, the rider should rise or sit in rhythm with the motion of the horse.

When the horse's front outside shoulder or leg moves forward, it signals that the rider should be coming out of the saddle. This movement correlates with the correct diagonal because it ensures that the rider is matched with the horse’s rhythm, effectively aiding in balance and communication between rider and horse.

In contrast, the other options do not specifically indicate correct diagonal riding. The hind leg being off the ground pertains more to the overall movement of the horse rather than the rider's diagonal. Even weight distribution relates to balance but does not directly help in identifying the diagonal. Finally, a transition to gallop changes the pace entirely and would not assist in determining the diagonal at a trot. Thus, recognizing the forward movement of the horse’s front outside shoulder or leg is the most accurate method to establish if the rider is on the correct diagonal.