I've always wondered...
They seem to have the cameras already in place on some of the courts. All the other Grand Slams use it but RG.
Of course, the ball leaves a mark on the clay and that makes it possible for the umpire to check whether the ball is in or out, but errors can occur and the umpire wouldn't have to leave his/her chair.
The funny thing is that even after the umpire checks the mark, they often show the camera shot. What if the latter is different from the umpire's interpretation?
I think it would make life easier - and avoid potential conflicts - at RG if they used the challenge system there. At least, RG would be on par with the other Slams. What do you think?