George Russell says his test in Mercedes' W10 Formula 1 car in Bahrain allowed him to give useful feedback to his struggling Williams team.
Mercedes junior Russell drove his regular FW42 on the first day of the post-race test, before moving to his parent team's machine for the second day.
He set both the fastest slowest times of the test in the combined order.
"It was an incredible experience and an experience not many drivers get to try," said Russell, when asked by Autosport about testing the two cars back-to-back.
"They [Mercedes] are currently leading the world championship, are a world championship-winning team and arguably the fastest car on the grid at the moment.
"So, for me, for us in our current situation where we are at the back, it was a great opportunity to know what we should be aiming for."
Russell said he could not share specific data with Williams's engineers, but was able to give the team a good idea of where its 2019 car was lacking.
"Obviously we did agree that I'm not going to come back and share confidential bits," he added.
"But I'm more than capable of coming back and saying, 'Their car is doing X in these corners and our car isn't and this is what we need to be working towards'.
"It was a very good test. We know they have more downforce than us but it's more to it than just having more downforce."
Asked if the FW42 was worse in every corner, Russell said: "I'd say the difference is as expected.
"You look where Mercedes are, you look where Williams are, the difference was absolutely as you'd imagine."
Russell drove Kubica's Williams during the test, but said he did not do enough laps to draw any conclusions about it.
Kubica complained during the Bahrain Grand Prix weekend that his chassis had an aero issue, despite ostensibly having the same set-up was Russell's.
"Obviously testing is one thing and racing is another," said Russel. "I only did 25 laps I think, only five of which were fast laps.
"So there was nothing really to conclude from that."