Nico Rosberg is pinning hopes of an uplift in form for Mercedes GP on an update package that is planned for introduction at the season-opening Bahrain Grand Prix.
Mercedes has not been a frontrunner in any of the tests so far, and Rosberg was only ninth-quickest at Jerez on Thursday - 3.2 seconds off the pace.
When asked about the car's apparent lack of speed, Rosberg said: "Yeah, but we expected that. This is an interim car, it doesn't have a lot to do with the car we will have in Bahrain.
"We just need to put miles on it. It's important to get the systems working, like KERS, the cooling, and to work on reliability."
Rosberg says it is impossible to judge where Mercedes GP are in the pecking order until it has the new parts in Bahrain - although its own step-forward in form will coincide with similar developments from rival teams.
"We have a significant step for Bahrain, so that's why I'm not looking at the times," Rosberg said. "The others might have a step as well, but it's impossible to say yet.
"My rear wing wasn't working today, and that takes away so much from the lap time. It's really early days."
He admitted today had been a complicated one for Mercedes.
"I could do many laps, that was positive," said Rosberg. "Unfortunately there were a few small problems that put us back. The rear wing wasn't working properly, a small gearbox issue stopped me at the end and a sensor issue stopped me before that.
"So it wasn't a perfect day, but we are learning, and also for me as a driver it is important to do many laps."
Asked if the problems that had affected Mercedes' pace at Valencia were reappearing at Jerez, Rosberg said: "In a way, yes. But at the same time they were happy to see it, because it confirmed something we had in Valencia that was not easy to confirm at the time.
"Now, with the problem I had today, it made us understand fully. They made me do some things with the car, like pull the clutch, and apparently that allowed them to understand one of the issues."