Like medieval military engineers did before them, the NOVA crew fine-tunes its attack using trial-and-error. Neel believes that if the sling is shortened, it will add arc to the stone's flight and give it more distance.
His hypothesis proves right: The next launch travels the right distance but lands a few feet to the wall's right. They shift the giant trebuchet just one inch to the left. This time they are on line but just overshoot the wall. They pull the sling in six inches and this time, it hits its mark.