IT IS considered to be one of the most reliable ways of calling a decision in sport. But two days before the biggest tennis tournament in the world is to start, university boffins have called the ball-tracking Hawk- Eye system into question.

A report from Cardiff University claims the pioneering device's margin of error is possibly greater than the public thinks since it is technically difficult to provide definitive data.

However, the International Tennis Federation tested Hawk-Eye in 2006 and an average margin of error of 3.6mm was recorded.

The federation will accept a margin of error of up to 5mm.

Nonetheless, the Cardiff academics claim this could be inaccurate - and the real figure could be either higher or even lower than 3.6mm.

It goes on to say that devices like Hawk-Eye could lead spectators to overestimate the reliability of new technology and its ability to give definite decisions.

But the Hampshire man behind the invention has dismissed the study's claims.

Managing director of Hawk-Eye Innovations and inventor Paul Hawkins said he believes the findings are motivated by a disagreement he had with the research team at Cardiff University.

He said: "Anyone living in the sane world would say Hawk-Eye is sufficiently accurate.

"No system is ever going to have zero margin of error but at some point you have to make a decision.What are you going to do - go up to the net and start having a debate or asking fans to phone in and vote?

"But isn't it wonderful that we live in such a developed world where university professors can spend their time researching something that doesn't need to be researched. Do they really have nothing more important to do?"

He went on to say that the people involved in this report had not had input from him, had not seen the device tested and had no links with professional tennis.

He added that Hawk-Eye's average margin of error of 3.6mm was vastly superior to the human eye - which can be inaccurate to a couple of centimetres - and, unlike people, technology is always impartial and never had lapses of concentration.

The device has now been tested thousands of times against a high-speed camera by the International Tennis Federation (ITF) and has, according to Dr Hawkins, never made an incorrect call.

Since its launch in 2000 Hawk-Eye has been used in a variety of sports and has recently had a great impact on the world of tennis.

During the first round of the 2007Wimbledon Championships Teimuraz Gabashvili made the first Hawk-Eye challenge on Centre Court while playing Roger Federer.

And in the final between Federer and Raphael Nadal, the latter challenged a shot which had been called out and - after referring to Hawk-Eye technology - the decision was reversed. A furious Federer demanded the machine be turned off, declaring the machine was "killing him". The referee refused.

After the incident,Mr Hawkins robustly defended his device, and The All England Club chief executive Ian Ritchie insisted they had carried out an "exhaustive"

series of tests before the tournament - tests that Hawk-Eye had passed.

He added the ball had landed in by 1mm and claimed that the naked eye was deceived because of the way a tennis ball presses and skids on landing.

Professor Harry Collins, who led the Cardiff University study, fiercely refuted claims that his team's research may have been coloured by a disagreement with Mr Hawkins.

He said: "This has got nothing to do with it.We decided to study Hawk- Eye and I approached Dr Hawkins for help, as you would expect, and he declined to help but that certainly had no influence on our paper.

"The aim of this study was to improve the public's understanding of science and statistics.

"I would say that in sport some decisions would be best made by a referee or umpire and some would be best made by technology.

"I think Hawk-Eye would be better used as an aid to an umpire, as opposed to a decision-maker."

He went on to say that he had published numerous reports on different kinds of technology which had been well received and this was just another system the university had decided to look at.

The paper entitled You Cannot Be Serious: Public Understanding of Technology with special reference to Hawk-Eye is due to be published in the journal Public Understanding of Science in July.