It’s time for the French Open again in tennis. I went once; it was thrilling. On those clay courts, line calls are made by examination of the mark that the ball leaves on the court. There’s no high-tech instant reply screen. An expert chair umpire jumps down and trots over to determine the ball’s trajectory and settles a dispute over whether it was in or out, and the point is decided. I found an old New York Times article about it interesting.