Rubens Barrichello described the first day of running of the Williams FW33 as "positive" after completing 77 laps in the new car at Valencia today.
The Brazilian lost track time when a problem arose with the motor generator unit in the team's KERS system that the team is confident can be easily fixed for tomorrow, but he was otherwise happy with the progress made.
This is despite admitting that the programme that he was working through on the first day - which included testing the new adjustable rear wing - made it difficult to judge the potential of the car.
"We learned a lot," said Barrichello. "The FW33 is a different car and it needs a different setup and a lot of understanding so today I was just sent out every time to cover miles. The balance of the car wasn't really good, but it's going to be very difficult to have a car that feels good with the amount of fuel that we were running."
Barrichello set the 11th fastest time of the day, 3.566 seconds off pace-setter Sebastian Vettel's Red Bull, but insists that it is too early to make anything of the timesheets.
He added that he was impressed with the design of the FW33, which features a very tightly-packaged gearbox that allows a very clean airflow to the lower section of the rear wing.
"The car is beautiful," said Barrichello. "The back end of the car is done fantastically. Right now, if you look at the times you would say it is 'too bad' but I don't think we can look into that because there is too big a difference of fuel load. I'm not concerned.
"There is more than three seconds between low fuel and what we are running. I would say that, from what we saw today, we can't compare it to the fastest times.
"Last year, I qualified outside the top 10 for the first race but I was, at one point, on the top of the timesheets in one of the tests. That shows how much the fuel can do. I just have to concentrate on the balance and see what it brings."