Max Chilton says he is encouraged by Marussia's progress after he set the fastest time during the first day of the second in-season test in Spain.
Chilton set a lap time late on the day on super soft tyres to beat his 10 rivals and put Marussia on top of the standings.
"Generally we’ve had quite a successful day and to end it in P1 is obviously a real bonus," he said.
"We’ve made steady progress throughout the day and to get the car to such a good place in terms of set-up, and then be able to see just how much we can extract from it, is a really big step from the race on Sunday to what we have achieved today.
"The conditions were pretty tricky this morning and on one occasion caught me out when I locked up and went straight on into the gravel. It’s always good to get some wet weather experience with the car though; there are quite a few occasions over the next few races where I can see that coming in quite handy.
"After the lunch break, once the weather had improved, we were really able to start working through the set-up improvements we wanted to explore further after the weekend.
"We went step by step through the programme, verifying everything we had concluded from the race here, and we can be really pleased with where we’ve got the car to. With another day of testing, I think we can leave Barcelona with the package in a really strong position."