Four days of testing in Jerez last week will have told the teams a lot – but only about themselves. Relative to their opposition, they will know very little more than the on-looking world – and that’s all to do with the ‘known unknown’ (to borrow a phrase from Donald Rumsfeld) of relative fuel levels.

The times that have the two Ferraris of Kimi Räikkönen and Sebastian Vettel out front, around 1sec quicker than the Mercedes, and with the Sauber of Felipe Nasr snuggled between them, mean almost nothing.

Almost, but not quite nothing. For one, the times of the Ferraris are quite quick relative not only to last year but also to the V8 cars of 2013.

In the equivalent test of last year Kevin Magnussen’s turbo hybrid 1.6-litre V6 McLaren was quickest at 1min 23.276sec. In 2013, Räikkönen’s 2.4-litre V8 Lotus set the pace at 1min 18.148sec. The new Ferrari SF15-T was therefore poised approximately halfway between the best times of 2013 and ’14. It was vastly quicker than the F14T went around there last year, the timing figures apparently backed up by the data on Ferrari’s own telemetry comparison showing apex and entry speeds, aero loadings, etc. So the new Ferrari is not a slow car – but is it a fast one? That of course depends upon the opposition.

Red Bull’s running was curtailed by a Renault engine issue – nothing serious, just a shaft in an ers cooling pump that couldn’t be re-engineered in the available time – and McLaren-Honda’s by all sorts of electrical gremlins. So take those two out of the equation and let’s assume that Sauber were running light, leaving us to concentrate on Ferrari, Mercedes and Williams. A lot of assumptions there, but that’s all we have at this point.

What we do know is that the best times of Räikkönen, Vettel, Rosberg and Massa came on runs of 10-11 laps. What we don’t know is how many more laps, if any, they could have done with the fuel they had on board for each of those runs. Each team has its own baseline fuel level for this sort of running, and it varies from team to team and from run to run. Some fuel close to the minimum required for the duration of the run, others prefer to replicate what would be in the car for an expected race stint for the type of tyre that is being used. Still others purposely over-load the car with fuel weight, trying to expose their weaknesses.

But let’s assume Ferrari, Mercedes and Williams each had comparable fuel loads. Then we have to consider the compound of tyres. Räikkönen’s time was set with a soft compound. Those of Rosberg and Massa came when they were on the medium – generally reckoned by Pirelli to be 1.5sec slower than the soft around here. Add 1.5sec to Räikkönen’s time and it puts him about on par with the Williams and around 0.4sec off Mercedes. But the intriguing one is Vettel. When he set his best time the tyres did not have the yellow stripes of the softs and this has led to belief that he was on mediums. If he was, then the Ferrari would appear to be very quick indeed. But it would also imply that – if they were on comparable fuel loads and the car was working properly when Kimi set his time – Seb was driving around 1.4sec quicker than Kimi. That is simply not feasible. Stories then went around that the tyres on Vettel’s car were indeed softs, but were un-marked. This would make a far better fit with the evidence.

So, what we think Jerez showed on a best-fit basis, but we cannot be certain, is that Mercedes is still setting the pace, but only by around half a second from Williams and Ferrari and that we have no idea at all yet of the relative pace of Red Bull and McLaren. We’ll probably find out a little more in the forthcoming Barcelona tests, but not until Melbourne will the real picture emerge with any clarity.