NEW YORK — A ball appears to land perfectly on the line and Anja Vreg practically leaps from her chair.
She's not sitting in the stands.
She's not even sitting on the same side of the street.
She does, however, have one of the best spots to watch the action during the first week of the U.S. Open.
Vreg is a review official monitoring a match on the screens in the office being used for video replay on the outer courts at the USTA Billie Jean King National Tennis Center.
The U.S. Open this year became the first Grand Slam tournament to have electric line calling on all courts. That was of particular importance to doubles players, who usually don't get to play in the stadiums where it was previously available until the later rounds.
"I think actually this is quite fair because it can change a match," said Pierre-Hugues Herbert, who teamed with Nicolas Mahut to win a match on Court 12 on Saturday.
Reviews on Arthur Ashe Stadium, Louis Armstrong Stadium, the Grandstand and Court 17, the Open's four main courts, are still conducted within those stadiums. But to enable the technology on the outer courts, the office was set up within the broadcast compound on the grounds.
Most fans attending the two-week tournament will likely never notice the small white door that simply reads "Electric Line Calling." But key points of matches can be determined within its walls.
"It's kind of a nondescript room and what goes on inside is very different," said Oliver Clough, a project manager for Hawk-Eye, the company behind the system that tracks the trajectory of each shot.
Unlike the stadiums, the smaller outer courts lack the capabilities to conduct the reviews. The review office was cheaper than building a spot at each court, and more in line with how replays are being conducted in other pro sports.
Each match is monitored by a two-person team watching four views of the court. Review officials such as Vreg are U.S. Tennis Association officials, while the engineer seated alongside her operating the system is a Hawk-Eye employee.
They can watch the action from 10 cameras positioned around each court and can hear audio of everything happening on it, and the review official is equipped with a microphone, telephone and radio to speak directly to the chair umpire when necessary. The goal is to be able to provide the view to get an in-or-out ruling in about 10 seconds, and sometimes they get a head start even before the umpire announces a player is challenging a call when they see a shot close enough that they believe it will be disputed, such as when Vreg sprang into position while watching a doubles match on Court 11.
The impact has been substantial. Clough said there had already been more than 1,500 reviews this year, 801 alone in the first two days of play. By contrast, there were only 459 challenges for the entire tournament in 2009.
"So that's the kind of scale that has happened here," he said.
Players would like to see even more. Lucie Hradecka, into the third round of doubles with partner Ekaterina Makarova, said the technology is a great addition and wished it had been available while playing in the singles qualifying tournament.
Clough said there were some 35 to 40 people in the room during the hectic first few days of the tournament, when every court was in use and every match going on at one time could be seen on the office's big screen. The workload has lessened with fewer matches on the schedule.
But the use of technology will only increase. Where the U.S. Open once could only rely on line-of-sight reviews, the video feeds and bunker setup have provided a way to make every court equal.
"We see it in a number of sports now. Pretty much all the American sports have review centers," Clough said.
"I think it's a natural progression for tennis to move to a centralized location on site."