Charles Leclerc ended the day at the bottom of the timesheets but was among those who accumulated the most mileage on Tuesday.
Despite the difficult conditions, the French rookie clocked in with 81 laps under his belt and the feeling of a job well done, despite a minor spin earlier in the day.
"First of all, it is great to be back racing after a long winter break," said Leclerc.
"Overall, it was a very positive first day of testing for me.
"Although the weather conditions were not ideal, with low temperatures and even some snow in the afternoon, I was able to develop a better sense of what the car behaves like on track.
"We completed a good number of laps, completing aerodynamic and mechanical tests throughout the day. The C37 has potential, and I look forward to driving again on my second day of test 1."
Sauber tech boss Jörg Zander was also satisfied with the result of the team's heavy workload on a day which he qualified as productive.
"It was another positive day of testing – despite the low temperatures and tricky weather conditions.
"Building on the data we collected yesterday, we continued our programme by doing set-up work and taking aerodynamic measurements.
"In the morning, we were not able to run as many laps as expected due to the weather. In the afternoon, we focused on long runs while testing different tyre compounds.
"It was important for Charles to get used to the new car as well as to the team procedures. Overall, a productive day."