The Hawk-Eye line-call system has been called into question at the Australian Open tennis championship after it failed to register a shot on centre court.
The ball tracking system was unable to pick up a shot in the fourth set of the Roger Federer-Tomas Berdych match, probably due to a heavy shadow over the line in question, leaving the Czech player furious.
The Czech was furious, while Federer, a long-time opponent of the system, says the incident had only confirmed his doubts.
The world number two says it's horrible and he doesn't like it.
Three of the four grand slams use the technology. The French Open is the only major not to use the system as the ball leaves a mark on the clay surface.
The system was first used at a grand slam at the 2006 U.S. Open.
The sport's governing bodies agreed last year that players will be allowed up to four unsuccessful challenges per set at any tournament that uses electronic line calling systems.
The Hawk-Eye technology reconstructs the ball's most likely path by combining its trajectory with images from cameras positioned around the court.
The International Tennis Federation were unable to comment on the latest incident when approached by Reuters.