Lewis Hamilton had a particularly low-key session in Barcelona on the second day of pre-season testing at the Circuit de Barcelona-Catalunya.
Taking the wheel of the new W13 for the morning, Hamilton managed just 40 laps over the four hours before the lunch break and the end of his scheduled time for the day.
With Hamilton finishing more than three seconds off the pace, Mercedes have explained why he managed so few laps in comparison to the average 70+ laps that most drivers managed during their half-day appearances.
"We had a difficult morning with Lewis, experiencing a data logging issue that delayed our start and, in general, we were struggling a bit more with the balance," said Mercedes' Trackside Engineering Director, Andrew Shovlin.
"Some of that may have been set-up items that we were trying and some of it the harder tyres that we were running today.
"We managed to get a few runs completed and then, unfortunately, had a sensor issue that prevented us doing further performance work, so we stopped early for lunch in order to fix it."
Russell takes over for the afternoon session
With Hamilton jumping out of the car at lunch, George Russell took the wheel for the afternoon. He managed 66 laps, exactly the length of a Grand Prix distance, and finished up the day fourth on the timesheets.
"George had a more productive session in the afternoon and we got through some useful set-up scans and completed some of our tyre programme," Shovlin said after the conclusion of Russell's programme.
"We've still got plenty of issues to work on from a performance point of view but we are continuing to learn with every run which in turn will make us faster.
"We've got a busy day planned for tomorrow, plenty more setup work and a first look at some of the softer rubber compounds for this year."
Testing resumes at the Circuit de Barcelona-Catalunya at 09:00 local time on Friday.
With F1 pre-season testing getting underway in Barcelona this week, our journalists Dieter Rencken, Mike Seymour and Thomas Maher look ahead to what to expect.