New Mercedes recruit Valtteri Bottas has admitted he has found the process of switching teams a harder challenge than expected.
Bottas has replaced Nico Rosberg at the world champions following the German's shock retirement and made an instant impression in pre-season running by setting the fastest time at the Circuit de Catalunya.
But despite topping the timesheets at the first Barcelona test, Bottas, who has only previously driven for Williams in F1, says he has been surprised by the challenge of adapting to new surrounds.
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"I'm definitely feeling more comfortable with the team every day but there is still work to do. Changing teams is maybe a slightly bigger thing than l initially thought it would be. But it's not a hurdle you can't get over and I've been working pretty flat out to get comfortable.
"That's why everything has run quite smoothly and I'm sure next week we will make big progress. And before Melbourne I will have time to go back to the factory and analyse everything and I'm confident we will be ready so I'll be completely part of the team before Melbourne."
Bottas added: "I am the type of driver who likes to understand everything what is going into the car and what effect it has. With how the car behaves there is still a bit more to do."
Bottas' challenge is in contrast to the benefits of familiarity being enjoyed by Hamilton as the Englishman approaches his fifth season with Mercedes.
"What Lewis has as an advantage is that he has been part of this team for a long time, he knows exactly how the team works, and he commented after the first run in the new car that it had pretty much the same behaviour to the old car. But l would rather join a team at this point than last year.
"Having a new team-mate, there is always something to learn and I'll definitely be watching Lewis closely. It would be stupid not to."
Bottas has been installed as second favourite for the world championship in the wake of his performances at Barcelona but believes he still has plenty of scope for improvement.
"I can learn massively with the engineers. This is an opportunity for me to get to the next level with my performance with all the technical understanding. There is so much information coming in and nearly as much as I can take in so it's very interesting."
The Sky Sports F1 Digital team will be providing live commentary from dawn until dusk for all days of winter testing while Sky Sports News HQ will also deliver live updates from trackside.