They claim it's no secret weapon, but a high-tech scrum machine built by a company that makes flight simulators means France already know what the Wallabies pack will throw at them this weekend.

Tucked secretively away in the state of the art Centre de National Rugby, south of Paris, is a 200,000 euro computerised scrummaging tool which was designed with a medical professor as part of a rugby safety program.

It's also used each week by the French pack, whose scrum coach Didier Retiere can dial in every move made by Ben Alexander, Stephen Moore, James Slipper and co.

"We decided to build a machine able to give us information about what happens during the scrum," Retiere said.

"After that we said maybe we can do training sessions on it."

They've done both and the results make interesting reading.

For instance, the impact of a Test pack hitting in a scrum comes in at 1,400kg.

That's at 80 thousandths of a second, too fast for the brain to react if a front-rower is in the wrong position.

The results have led to a ban on impact in scrums in French community rugby.

Les Bleus, who arguably already boast the best scrum in world rugby, have been using the machine since June, programming it to mimic their opponents' set-piece, down to their collapses.

If Australia thought their iffy scrum was going to be up against it at the Stade de France on Saturday night (0645 Sunday AEDT), they may not have seen anything yet.

"I think it's improved (the French scrum)," Retiere said. "It gives confidence to the player because they're seeing that the scrum on the simulator is more difficult than the game."

Plans are underway to use the knowledge gathered by the prototype simulator to build an updated version.

Retiere, who is also in charge of the research project, says Australia and France approach their development of forwards differently.

"You take a pretty good rugby player and you make them become props," he said.

"InFrance, we take props and we try to make them become a good rugby player."

But, as much as it may hurt him to say it, Retiere is playing down the importance of the scrum in the weekend's clash with the Wallabies.

"It's like playing cards and you've got one ace in your game," he said.

"If you put it anywhere it doesn't work, you have to use it really carefully.

"The good player sometimes with a bad hand is able to have a great game.

"That is the problem for us. We know we've got maybe a good card in our hand but we have to use it at the right time.

"(Australia) have other good cards."

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