Wise men refrain from reading too much into the times set at winter testing, while fools rush in and make assumptions for the season based on pace set out of any context.

But while the times themselves can often mask more than they reveal, one statistic that can't be massaged or hidden is the number of laps completed. With the restrictions on in- and pre-season testing, it is crucial for teams to get as many miles as possible under their belts in the limited time available.

And that's in an ordinary pre-season. This year, with the seismic shift in technology (and particularly the ultra-complex power units in need of serious cooling) getting miles on the clock is even more important than it has been in years past.

Instead of being a battle between the teams, Jerez has been a battle of the engine manufacturers, with more attention being given to the number of laps each OEM has logged than those completed by any one team.

Day one saw Ferrari come out on top, with Kimi Raikkonen and Esteban Gutierrez managing 38 laps between them. Mercedes were next up with 36, while the Renault power unit had logged 19 at the end of the first day. But day one was always expected to be problematic, with many prophesising endless explosions and a total lack of running.

On the second day of the Jerez test it became clear that there was a significant difference between the Renault unit (19 laps) and the Ferrari and Mercedes units (100 laps and 212 laps respectively), with the latter two able to log significantly more miles over the course of the day. The bulk of the problems suffered by Red Bull, Toro Rosso, and Caterham were all linked to the power unit, which implies reliability issues at a time when all OEMs have asked their customers to run with the wick turned down.

Rumours about the efficacy of each unit were doing the rounds all winter, and while it's hard to get to the kernel of truth inside each one the sense was that none of the 'engines' were able to go full race distance shortly before Christmas, hence the need to keep the power down while trying to collect as much mileage as possible.

Based on the number of laps completed over the past two days, Ferrari and Mercedes (and their customers) have been able to find a balance between the amount of performance needed to generate useful data, and the reliability required to harvest enough of it, while Renault's customers haven't been quite so lucky.

It's far too early to make assumptions of a terrible year for the Renault-powered teams. The French manufacturer has a wealth of experience, knowledgeable staff, and excellent facilities with which to get to the bottom of the issues they're currently suffering. But there's no denying that it's not the best of starts, with teams and engine manufacturer alike short of the sort of data they need to ensure they become - and remain - competitive.

Kate Walker

Kate Walker is the editor of GP Week magazine and a freelance contributor to Crash.net. A member of the F1 travelling circus since 2010, she keeps an eye on the behind the scenes wheeling and dealing that makes Formula One a political melodrama.