If Major League Baseball’s new instant replay system had been in place for the entire season, it would have been used about 18 times so far to determine if a home run had been hit. In some of those instances, calls allowing the homers would have been reversed.

During a behind-the-scenes demonstration of the replay technology at MLB Advanced Media in Manhattan on Wednesday, Jimmie Lee Solomon, an executive vice president, said research indicated that about 18 home runs would have been subject to reviews. That amounts to about a home run review a week across the first five months of the season.

Once the replay system debuts with games played on Thursday, there will be as many as three people monitoring every game at the Advanced Media offices. When an umpire crew chief decides he needs to see a replay for a call, he will leave the field and use a telephone that links to one of the game’s monitors in Manhattan.

Because the center has access to every broadcast feed of a game, it will usually have two or three replays of a play from each network that is televising it.

Three seconds after a replay is shown by a network, the center will be able to deliver it to a crew chief. The umpire can ask to have the replay paused, repeated or frozen. Solomon said any uncertainty about a call was expected to take about 2 minutes 30 seconds to resolve through a replay.

Some networks, like the YES Network (Yankees), SportsNet New York (Mets) and NESN (Boston Red Sox), are affiliated with the teams they cover. Solomon was asked about the possibility that a network would withhold a replay if it showed something that worked against the team it is aligned with.

“We don’t expect anybody is going to impact the game in that fashion,” Solomon said.

But if MLB officials believed that happened, Solomon said, “We would impact them through the commissioner’s office” with some form of discipline.

While it seemed strange that baseball would institute the replay system with about a month left in the season, Solomon said, “You can’t ignore the technology we have now,” so it did not make sense to wait. Solomon said implementing the system today would allow everyone involved to get comfortable with it.

Still, as much as commissioner Bud Selig praised the technology on Tuesday and as much as Solomon did on Wednesday, Solomon reiterated that baseball had no intention to use replays beyond home run calls. Replays will determine if a ball has cleared a fence, if a ball was fair or foul or if a fan interfered with a play.

“The commissioner made it clear this is limited use of replay,” Solomon said.

Once an umpire uses a replay to make a decision about a play, a team will not be allowed to show the play on the scoreboard. Solomon said camera operators would be prevented from showing footage of an umpire reviewing the replays.

Red Sox manager Terry Francona said he would have preferred to see MLB add a fifth umpire to each crew and let that umpire watch the game in the press box, where he could study replays and make decisions on plays that need to be reviewed. Francona guessed it “would take 10 seconds” to resolve each play if that format was used.