It's usually fairly simple to tell when a goal is scored in a World Cup match: it swooshes into the back of the net, ricochets off a goaltender's hand or at least trickles across the white goal line.
Sometimes, though, it's not quite so obvious. These rare moments, when everyone in the stadium has a different opinion on whether or not a goal was scored, usually dependent on which team they follow, can be the difference between winning soccer's biggest prize and going home empty handed. That was the case in 1966, when England's Sir Geoff Hurst sent a shot off the cross bar. It bounced to the ground at a 90-degree angle, landing just over the goal line.
Or maybe it landed just in front of the goal line, as the German team believed. The referees conferred, ultimately deciding that it was indeed a goal. England went on to win its only World Cup crown.
In 2010, with the archrivals facing off in an elimination game, it happened again, but with a very different outcome. England midfielder Frank Lampard's strike in the 38th minute bounced down off the crossbar and spun back into the field of play. Replays showed it crossed the goal line and should have evened up the contest at 2-2, but the officials ruled it a no goal. Germany ultimately won 4-1.
Now FIFA referees are finally going to have a little help judging whether the ball has crossed the plane of the goal line. For the first time, they'll have the aid of goal line technology.
The technology relies on 14 high-speed cameras placed along catwalks in the upper levels of the 12 World Cup stadiums. Seven cameras monitor each goal line. All together, the images from the cameras create a 3D record of the ball's movements.
The referees will be wearing wristwatches that are connected to the system, and will be alerted within one second if the ball crosses the goal line.
FIFA tested several technologies during the 2013 FIFA Confederations Cup, a smaller-scale tournament that was also hosted in Brazil. Sixty-eight goals were scored during the trial period, though none were controversial.
Players past and present say the technology is a welcome addition. In 2013, when the English Premier League started using a similar system, Hurst said it was about time.
"If we had this system 50 years ago, it would have shown quite clearly the ball was at least a foot over the line," he said. "Germany have been arguing the toss ever since but I will never tire of talking about it. They can't take it away now anyway. It is in the book."