Felipe Massa feels the new Williams FW37 is a stronger car than last year's Formula One challenger, but he thinks it is still too early to know where his team stands.
"We feel some improvements compared to last year in some areas where we were not very strong, which is positive," Massa told reporters at the end of the second day of testing.
Massa was third quickest in today's session in Barcelona, just over a tenth of a second slower than pace-setter Daniel Ricciardo.
"The car behaves well but I think it's a little bit too early to say where we are compared where we are compared to the others, so we keep pushing.
"We are still trying to put as many new parts for Australia that we don't have yet, and we still need to understand step by step and then when we have everything in the car we can look at where we are compared to the others."
The Brazilian, whose team had a very strong 2014 season, thinks there is still potential to get stronger before the start of the season.
"The car has good potential, but you know where you are when everybody is on the same fuel and on the same tyres, and then you can look at the laptimes and understand where you are compared to the others.
"I think even if you feel your car is good then you see all the people is doing much quicker laptimes than you it's different.
"I don't think that's the case, but anyway, when we get to Australia then we'll understand where we are.
"I think things are going in a positive way."