At The U.S. Open (Page 11)

How was the team to proceed in the light of this surprising and confusing development? In consultation with Engineer Jim Pallis in California, Eric Chattot investigated the problem. By going back and forth between the decks, he was able to determine that the spin rates were in each case double on the viewing deck as opposed to the high speed system. For example, a Pete Sampras first serve appeared to spin at 1800rpm on the high speed deck, but the same serve measured twice that or 3600rpm on the team's additional viewing deck. How could this be explained?

The answer lay in the unique capabilities of our high speed system! A video frame is actually composed on two images, called fields, that combine when viewed together to create a single image in a frame. In order to record 250 pictures in a second, the high speed video engineers had actually found a way to make each field record as an individual picture or frame!

A normal viewing deck works by combining two fields into one frame. This explained the difference! The team's viewing deck was actually combining two fields into a frame. In effect, it was only seeing half the pictures!