Valtteri Bottas feels that Mercedes' revised W10 has moved the team forward although he is unsure if it has made enough progress to rival Ferrari in Australia.
As it entered the thick of its preparations for the 2019 season, Mercedes rolled out a heavily updated W10 Silver Arrow at the start of the second week of pre-season testing in Barcelona.
Bottas says the new specs have improved the car's consistency in terms of the "massive" handling issues - as labeled by the Finn - that frustrated the German squad's first week of testing.
"It is better. But if it's enough, that is the big question mark," Bottas told the media in Barcelona.
"I definitely feel improvements since last week with the stability of the car, and with the overall downforce of the car.
"But we definitely feel that we haven't unlocked everything that there is to unlock.
"It's not the perfect car yet. Definitely we feel the potential is there. Maybe it's another car that has quite a small sweet spot, but once you hit it, it can be very quick.
"We are learning massively every day, I feel like it's been a good step, every time I get back in the car it gets better.
"I hope I can feel that again this afternoon and tomorrow and hopefully for a bigger step in Melbourne."
Progress is in the cards for Mercedes, but it still hasn't been enough for Bottas to change his stance from last week, when he claimed that Ferrari had the upper hand over the Silver Arrows outfit.
"They still seem strong. Obviously as always from testing to Melbourne, a lot of things can change but they do have a strong package," he added.
"I still think we do need to unlock more from the new package to be able to really compete with them properly."