Seeing a chair umpire jump down to the court, scamper across the clay and point out the mark of a ball is one of the great traditions of the French Open.
The scene adds to the spectacle. A sense of anticipation hangs in the air, whistles or cheers from the Paris crowd - depending who the decision is for - accompany the official to the spot.
But, in a sport of high stakes and fine margins, is it time to stop relying solely on the human eye to decide crucial points?
At the recent Italian Open, Britain's Andy Murray was annoyed when a line call went against him because the umpire ruled the ball mark was on the line.