Originally Posted by RANDY IN INDY
How accurate is this technology?
The physics involved are basically lift. So you basically get a measure relative to what would have happened differently than if it was only gravity affecting it. The spin in the ball affects the flow of air around it. For a fastball with backspin, this creates a pocket of low pressure above the ball, which results in a small amount if lift - same principal as a plane's wing.
So instead of falling 40 inches it only falls 34 inches, meaning it had 6 inches of "rise".
(I know you probably know that, was for everybody's benefit)