It looks like it has been a long time since you posted this... if you're still curious, here you go!
My experience of this drill comes from a video "The Art and Science of Teaching the Pole Vault". In this video, Alan Launder, a popular Australian coach and author of "From Beginner to Bubka", explains the drill as finishing 20 short, powerful high knees within 20 m or about 65.5 ft. The goal is to not finish early (18 or less steps) or not finish at all (21+ steps) when you do this drill for 20 m, while still having good form. However, the form comes first, and then the control of steps.
The form consists of high knees that are powerful, yet quick. The athlete shouldn't be pounding the floor with their feet in order to obtain the power, but they should be able to make a 90 degree (parallel to the floor) with their thigh/knee, and have their toe dorsiflexed (toes on the drive knee's foot pointing up). The movement must be quick enough to cover twenty steps within the distance.
This drill emphasizes form for running and take off, as well as conditioning your body to memorize this form naturally. That is, you won't have to think about this when you vault and thus can focus on other more important aspects of the vault. A powerful drive knee is key in the vault, and I hope you know why.
If anyone thinks I am incorrect in some way, please post. I hope this helps you and anyone else who decides to check this out!