Posted for "Rick Lafford" <gliderguy89@earthlink.net>:

 I believe Chelton data is based on a GPS fix whereas the pylon judge has a
 visual fix upward through the pylon. When it comes to a close call, I've
 been made to understand that multiple judges at the pylon might confer
 before rendering an official call.
 
 Your mileage might vary ....
 
 Rick