As they bounced the balls next to a tape measure taped to the wall they found it difficult to say the exact height of the rebound without any real accuracy. So what did they do? They did what any self-respecting college junior would do in a science class, they pulled out their cell phones and took pictures of it. This would never have occurred to me.
But they didn't stop there. They realized that if they used the slo-mo video feature on their cell phones they could slow the motion down so that they could actually see the elasticity of some of the ball as they hit the ground as well as the exact height of the rebound. Isn't that amazing and wonderful?