Andre Lotterer was "very pleased" with his first day with Caterham despite finishing slowest of all.
The German driver, who was drafted in just ago to help with development of the CT05, put in the laps in Friday's practice for the Belgian GP.
Quicker than team-mate Marcus Ericsson, he lost out to the Swede in the afternoon's session.
However, Lotterer's best time for the day, a 1:54.093, was only 0.043s slower than Ericsson's.
"I'm very pleased with today," said the 32-year-old.
"This morning's first practice was a good session for me; I got used to the car quite quickly and now I just need to optimise everything in terms of driving style.
"Considering it was my first time out, it all went according to plan and I was able to get a good feel of what it's like to drive the car. Now we need to keep working like this and continue improving the car.
"FP2 was another good session and everything went smoothly even though we had to stop a little bit early due to a technical problem.
"It's definitely been another learning process for me on the option tyre - I went out and I didn't know what to expect, but I think it went very well.
"We've been able to follow the programme as planned, improving while learning and trying to play with the car slowly.
"We did some long runs and I'm certainly starting to feel comfortable with everything, even though I'm still in the learning curve."