The Hawk-Eye system is broken in a number of ways. The 3.6mm is the average error on the calls, which means that some of the errors could be much greater. The creators ought to release what the 90, 95, and 99% confidence intervals are. If the average error is 3.6mm, the 90% confidence interval could be 10-15mm, and even more for the 99% CI. The way the challenge system works in football is the way it should work here: the burden of proof is on Hawk-Eye to over-turn the umpire. That means Hawk-Eye needs to be within a certain confidence interval on that call; if it isn't, it shouldn't count. If we're going to have it, I have no problem with the players having challenges; however, making calls shouldn't be their responsibility. The officials should be able to review plays as well, and should not defer to asking the players to "challenge" the call. That misplaces responsibility. I tend to think the entire thing is just a big gimmicky waste of time and money. The speed at which the simulation is shown is slowed down for the entertainment of the audience. Furthermore, the entire thing is just a bunch of calculations, based off of a number of data-points; I doubt it accurately accounts for the spin of the ball or the wind. It was shown to be inaccurate on clay, when it frequently was shown wrong by the marks. Federer, Nadal, and Safin are all against it. That means that not a single player who's won a slam since 2005 supports Hawk-Eye. That ought to tell you something.