Tim isn't right. 3-4 mm is the margin of error for Hawkeye. The system here has a larger margin of error, which is why they can't use it.
Rafa thought it was out, but did not show it. Pascal Maria came down, it looked to be the only mark in that area, and he saw it out. Yet Hawk-eye showed it in by a a couple of millimeters.
I trust the mark and the umpire more than Hawk-eye. Even when calibrated precisely, it has a 3.5 millimeter margin of error. And since they are not using it here, I'm not sure that the calibration is precise as it might be if it were in official use.
There is a good reason they don't use Hawk-eye on clay. They don't want situations like this, which may prove that Hawk-eye is not as "reliable" as people think. It is pretty reliable, but it does have that margin of error.
But an actual mark, as long as it is the correct mark, is even more reliable.