Did the ball cross the line? It's a question which football fans have been asking at least since the 1966 World Cup final, when England striker Geoff Hurst's extra time goal against Germany was given by a Swiss referee on the advice of his Soviet linesman.
World governing body FIFA has been trying out two technologies and will put them to the tournament test at the upcoming Club World Cup starting December 6 in Japan with a view to using the most accurate version at the 2014 World Cup in Brazil.
A last-16 match at the last finals two years ago in South Africa went a long way to convincing FIFA that the technology had to come to the rescue after England's Frank Lampard had what appeared to be a perfectly good goal ruled out against Germany.
The non-award of his effort ultimately went some way to presaging a 4-1 loss for Lampard's side, prompting the game's authorities to accept that there had to be a technological leap of faith to prevent such miscarriages of sporting justice.
Two systems -- one German, one English -- have been certified by FIFA and are now fighting one another for the right to be used in Brazil in two years' time.
First there is GoalRef, which uses magnetic fields and a special ball which will be tested at the stadium at Yokohama during the Club World Cup. The other, Hawk-Eye, is based on deploying cameras in similar fashion to that already prevalent in tennis and cricket.
The latter will be used at the Toyota stadium.
GoalRef is the brainchild of researchers Fraunhofer Institute for Integrated Circuit in Germany and the second has been created by Hawk-Eye Innovations in Britain.
"At the end of January we will discuss things with the two providers of their technology, and if there is a third system we will decide in February or March which will be used at the Confederations Cup" starting in June," said Christoph Schmidt of FIFA, who has just visited the Soccerex exhibition in Rio de Janeiro.
FIFA indicates the system which gets used for the Confederations Cup will not necessarily be guaranteed to be retained for the World Cup's 12 venues a year later.
During Soccerex, FIFA Secretary General Jerome Valcke defended the recourse to technology and explained that the system will sent a signal to referee's stopwatches -- with a one-second delay.
But Valcke says the referee will be the only one to see the information and the ultimate decision will fall to him, a better system, he suggests, than stopping the action for several seconds or longer "to watch a video or to say if a goal has been scored through handball".
In due course, FIFA hopes the system will evolve and be sufficiently accurate - and affordable - to be used in domestic leagues.