I don't know if yous have it but right now in the Australian telecast they use a program called Hawkeye which shows the ball mark on close line calls
so why not just use that instead of having inaccurate calls from linesman and umpires when you can have flawless accuracy with calling the shots? it takes something liek 0.02s for the program to determine the mark. all you have to do is wire up an audio device to it to announce the call. umpires can just call the scores
We've discussed it here before and I agree with someone (forgot who it was) that maybe it's too expensive to install on all the courts, especially in a Grand Slam. But who knows? Maybe the Slams can afford it. It sure would end those "...the bad call was the turn-around" kind of matches.