Ross Brawn is pleased with the progress Mercedes made in this past week's Barcelona test but says there's still "a lot" to do.
Nico Rosberg and Lewis Hamilton shared the driving duties at the Spanish track, clocking best times of 1:22.611 and 1:22.726.
That put them sixth and ninth on the overall timesheet, less than a second behind McLaren's Sergio Perez.
"Overall, we've had a good week in Barcelona and achieved the program that we set ourselves for this second test," he said.
"The rain was a little unfortunate; however, we made the best of the conditions and were still able to take some useful data out of the day.
"Nico and Lewis are becoming more familiar with the car and its behavior as each day progresses, and Lewis is settling into the team very well.
"Both drivers are providing excellent feedback which is pushing the development of the car both here and at the factory, and it is very rewarding to see their enthusiasm and commitment."
Mercedes will return to the Circuit de Catalunya next week Thursday for the final four days of pre-season testing before the season kicks off in Australia on 17 March.
"We now have just four days of testing left until the first race in Australia, and a lot of work will be done before we return to Barcelona next week."
