Formula 1's first proper in-season test for four years kicked off at a wet and overcast Mugello on Tuesday morning.
With so little to separate the frontrunning teams so far in 2012 - with the true competitive order of the front-runners still not clear - the three day test has been billed as a vital element in determining the next stage of the championship battle.
And although the teams would have preferred dry conditions for all three days, the early downpour could prove just as useful to help them get a better understanding of the wet and intermediate tyres - on the back of the surprise Fernando Alonso victory over Sergio Perez in the rain-hit Malaysian Grand Prix.
Much of the focus of the three-day test will be on Ferrari's Alonso, who will get his first taste this week of some of the F2012 updates that are being brought to the Spanish Grand Prix.
Speaking after a fans' day at Mugello on Monday, Alonso said: "The championship is proving to be a real battle, but even if it's tough, the aim is still to win."
Mark Webber (Red Bull), Kamui Kobayashi (Sauber), Jean-Eric Vergne (Toro Rosso) and Charles Pic (Marussia) are the only regular drivers doing a full day's running on the opening day.
McLaren, which has played down both the significance and relevance of the test, has opted to split the opening day between regular test drivers Oliver Turvey and Gary Paffett. Turvey will run in the morning, before Paffett takes charge for the afternoon.
Mercedes will operate a similar split, with China race winner Nico Rosberg being followed in the afternoon by Michael Schumacher.
Lotus, Force India, Williams and Caterham will all make use of reserve drivers on the first of the three days.
Jerome D'Ambrosio will take charge for Lotus, while Jules Bianchi - who suffered a costly crash for Force India during pre-season testing at Jerez - will resume testing duties for the Silverstone-based squad.
Valtteri Bottas and Rodolfo Gonzalez will meanwhile take the reins at Williams and Caterham respectively. Only HRT has opted not to run at Mugello.