The challenge system is a joke. Why are there not more stringent rules about its use (especially today, when it literally decided the match)? Signaling to your box (as Del Potro was doing) before challenging should not be allowed. Federer was completely right to complain that Del Potro was taking too long. There needs to be a rule regarding how much time can pass before challenging! The chair and lines officials also did a pretty lousy job. I particularly enjoyed when some guy in the crowd yelled out a call (correctly) that all the on-court officials had missed. The chair allowed Federer to challenge and then decided to give Del Potro a 1st serve despite the ball being out because of the "delay." Even worse was when Federer hit an ace and Del Potro apparently saw some distraction (though made no motion to play a let) and the chair made them replay the point. Also, am I the only one who suspects that thw challenge system might not be completely accurate. Wouldn't it be more logical to use it for ALL calls or not to use it at all? Nonsense. EDIT: I'm going to present this thread to the Hawkeye creator via e-mail. Math, computer and physics guys please feel free to post some questions regarding the system. If we have doubts about the system, let's try to get some answer!