A pinch of salt. That’s what any assertions from Formula 1 pre-season testing need to be taken with, particularly on day one.

But at the end of Monday’s running, there appeared to be one firm conclusion that we could take away.

For Ferrari, things appeared to go very well indeed at the Circuit de Barcelona-Catalunya on Monday as Sebastian Vettel topped both the timesheets and the mileage charts.

Following a shakedown of the new SF90 car in Barcelona on Sunday, Vettel hit the ground running early on Monday morning, quickly dipping below the 1m20s barrier before whittling down to the 1m18s before the opening session was complete.

Setting his fastest time on the C3 compound tyre – equivalent to the Soft used by Pirelli last year – Vettel was able to go 1.2 seconds faster than the best time from last year’s opening test, and was just 0.9 seconds back from the fastest time overall from 2018 pre-season.

At 169 laps, Vettel also completed more laps than any other driver, closing in on three race distances. Unsurprisingly, he was pleased with how his opening day had gone.

“We couldn’t have hoped for a better day,” said Vettel. “I think it was unbelievable. The car was working really well, we had no issues slowing us down, we did the programme just the way we wanted, we were able to squeeze a little bit more out even.

“It’s very early. It’s the first day, and it’s meaningless in a couple of weeks, but for now, huge compliments to everyone in the factor and how they have tackled the new regulations.

“What they put on track today is very close to perfection for the first day of driving.”

Ferrari’s pace caught the eyes of many through the paddock, including those of Mercedes’ team boss Toto Wolff. The team had opted to focus on long runs throughout Monday as it split duties between Valtteri Bottas and Lewis Hamilton, with the pair ending up two seconds down on Vettel’s time. More crucially, they completed a combined total of 150 laps – the second highest for any team.

“You need to be disciplined because we’re all keen to look at lap times, you want to be quick, and on top of the leaderboard, but it’s not the purpose of the test,” said Wolff.

“It’s to go through all the parts you want to look at, look at what the data and sensors tell you.

“I’ve seen the time. It was very quick, two seconds quicker than anyone else. Definitely, the Ferrari has been going quick this morning.”

In a similar fashion to Toro Rosso 12 months ago, Red Bull enjoyed a very productive first day of running with Honda as Max Verstappen neared two race distances in the RB15 car.

Despite a brief scare when the car lost power pulling out of the garage through the morning, Verstappen ended the day fourth-fastest – but the 128 laps on the board were the greater point of interest for team boss Christian Horner.

“The main focus is mainly getting miles on the board and understanding that complex marriage between engine and chassis to make sure both our working in harmony which seems to be working well so far,” said Horner.

“This week is all about getting miles on the board. These cars generate a huge amount of data now which is broadcast live to our factory in Milton Keynes, so there is a team of engineers pouring over the data.

“You are looking to learn about the characteristics and understand the strengths and weaknesses of the car which then denotes the direction for the future months ahead.”

Added a coy Verstappen: “Everything was working quite well. We did quite a lot of laps. I’m happy about that, but it’s still the first day so you can’t really comment a lot.”

McLaren was left pleased with its efforts on day one in Barcelona as the MCL34 car completed its first running, having not previously been shaken down. Carlos Sainz Jr. had one stoppage on-track in the early part of the afternoon, but otherwise had a trouble-free day, finishing second fastest on the C4 tyre.

“You could see some smiling faces, especially this morning when we left and started to put laps and laps on without any issue or long car stops,” Sainz said.

“I think that was a very good way to start and this afternoon we completed some long runs and we finished the day on red flags at six o’clock, so it was a good way to start.”

The only other team on-track in Barcelona that had yet to complete a shakedown was Racing Point, who had a more troublesome day. Teething problems with the RP19 limited Sergio Perez to only 30 laps, but the Mexican was nevertheless pleased with his initial findings.

“Today was better than expected when I first run the car. Everything that we expected in terms of grip, performance, and so on, on previous days in the simulator, was a lot worse than what we had today,” said Perez.

“Although it was a very short run, I’m happy with the start, and think we got a good baseline, and there is a lot of room to improve, a lot of room to understand and learn from this new car.”

Kimi Raikkonen’s day behind the wheel of the Alfa Romeo C38 may have started and finished with red flags – the first for a spin, the last a deliberate dry fuel run – but he too managed to break the century mark on the lap counter, lapping just shy of Verstappen’s time.

In fact, pretty much every team finished its day with something to be pleased with. Romain Grosjean recovered from an early stoppage in the Haas VF-19 to finish the day P3 with almost one race distance complete; Daniil Kvyat reported a “good baseline” with the Toro Rosso; and Renault, like Mercedes, prioritised long runs as Nico Hulkenberg and Daniel Ricciardo split duties.

And while the nine teams running in Barcelona all appeared fairly content with their initial findings, Williams found itself a world away. As the final build of the new FW42 car continued back in the UK, team personnel - and the Robert Kubica fans present at the track - were left waiting on news of when they would finally be able to hit the track.

Having already cancelled a planned shakedown over the weekend and pulled out of Monday’s running, the team issued a statement saying it was “more likely than not” to miss Tuesday as well.

Word in the paddock is far from positive. Deadlines have been missed, team morale is low as they work long hours to get the car finished, and concerns are that the “next-gen Williams” promised by deputy team boss Claire Williams for 2019 could be even further adrift than last year.

With the likes of Toro Rosso and Alfa Romeo appearing to grow in strength, a step forward was crucial for Williams to end stand still relative to its rivals, let alone to close the gap. And losing at least one-quarter of its pre-season running is very worrying indeed.

Even if the team were to get the car built tomorrow and down to Spain in time for the start of Wednesday’s running – which seems like a best-case scenario right now – the lack of a shakedown could leave Williams waiting until next week before properly hitting the track with the FW42.

We may not be able to glean many certainties from day one of testing in Barcelona, with positive noises coming out of every team running on Monday. But there appears to already be one safe bet brewing at the very back of the grid that could set the tone for the year to come.