More than US$10 million has been spent wiring the 30 big-league ballparks with cable that will transmit the images from at least 12 cameras at every site, and Major League Baseball says it will take just 400 milliseconds for each image to arrive at the command centre.

All in an effort to prevent the type of botched calls that cost Detroit's Armando Galarraga a perfect game in 2010.

"I'm happy for the managers," said Joe Torre, an MLB executive vice-president overseeing the new system. "Maybe it will keep them from having one or two more sleepless nights if they are able to grab one and overturn it."

Inside the sliding glass doors at the offices of Major League Baseball Advance Media, the room has its own power supply in case of a blackout - with batteries as a second auxiliary - and a stand-alone heating, ventilation and air conditioning system that keeps the temperature at 22 degrees Celsius. Mobile phones do not have reception.

There are dozens of televisions, more than enough to make it resemble Nasa's mission control. Outside the room, next to a modernist black sofa, is a 55-inch NEC screen, with another just inside the entrance. Walk in, and there is 65-inch Pentus TV on your left.

On each side are three stations, each to be staffed with a technician on the left and a major league umpire on the right. Three more "floater" stations stretch across the back wall.

Every station has four 46-inch screens - three Planars for each pod, with a higher-quality Sony directly in front of each umpire's seat. The umpires will wear headsets and can push a button to speak with their colleagues at any stadium.

Fifteen Asus computer monitors are scattered about, four on a wavy table in the centre where supervisors will monitor the review umpires and up to 15 simultaneous games (there would only be the maximum if weather delays the action in the eastern half of North America).

The nine circular overhead lights are kept low, the walls are grey and the carpeting is dark - all so that the televised images will stand out more for the umpires. There is a sink and a microwave - the food court on the first floor is filled with dozens of options.

"I'll see more games than the Fan Cave," quipped Justin Klemm, a former minor league umpire and big league fill-in who was hired last month as MLB's director of instant replay.

Baseball ignored replay even as it was first used by the NFL in 1986, the NHL in 1991, the NBA in 2002 and the Little League World Series in 2008. MLB took a tentative step towards replay in August 2008, when it first used video to decide boundary calls such as home runs at the top of fences or near foul poles.

Torre (who managed the New York Yankees from 1996 to 2007) long opposed video review, but changed his mind in October 2012, when umpire Jeff Nelson missed a call on Robinson Cano's two-out tag of Omar Infante at second base in the AL championship series, calling the runner safe. Detroit went on to win game two and sweep the Yankees. "That's when I realised that we certainly can't ignore the technology and the fact that this seemed to be what the people want or think they want," Torre said.

Eight umpires will be assigned to the replay room each week, with generally six on duty for a full schedule and each monitoring two games at a time.

When an umpire has a decision to make, screens for their other game will go dark. If an umpire has simultaneous challenges in both games, one will "cascade" to the next pod over.

Baseball established a "clear and convincing" standard for overturning calls. The replay decision will be either the call is confirmed, stands (if there is no conclusive evidence) or is overturned. Managers get one challenge per game, and if that challenge is successful, they receive a second. If a manager is out of challenges, from the seventh inning on an umpire can call for a replay on his own. In addition, home runs and plate collisions are subject to unlimited review at the discretion of the crew chief.

Baseball hopes it will take no more than an average of three minutes for the decision. The average length of a nine-inning game was a record two hours, 59 minutes last year. Torre said pace-of-game rules would be enforced more strictly.

"In order to make this thing work and not have it make the games longer is the fact that we have to start really disciplining and paying attention to the repeat violators," he said.

Open for replay challenges are force plays, tag plays, fair-foul in the outfield, traps in the outfield, hit batters, retouching, passing runners, ground-rule doubles, fan interference and home runs (at the umpires' discretion). Among the excluded decisions are ball-strike calls, check swings, foul tips making contact with the bat, baulks, interference and obstruction calls, the neighbourhood play at second on double plays, running out of the basepath or runner's lane, tagging up and catches in the infield. MLB says that among incorrect calls last year were 156 force plays, 60 tags on steals and 76 other tags - totalling 86 per cent of all missed decisions.

Torre said he expected more dropped balls during pivots at second base would be called safe rather than forceouts, and MLB would monitor phone traffic between team replay personnel and dugouts to ensure the video was not used for sign stealing.

About 75 umpires came to New York for training, and MLB sat down with all managers during spring training and had a conference call with them last week.

"I could tell you one [for which] I'm glad we didn't have replay," Torre said, an apparent reference to Richie Garcia calling a 2-2 pitch to Tino Martinez a ball in the 1998 World Series opener. Martinez hit a grand slam on the next pitch, and the Yankees swept San Diego. "I'm wearing that ring right now," Torre said.