Click here for full Tuesday testing results
Sebastian Vettel has topped the first day of the Spanish GP post-race test after working on qualifying issues which hampered him at the weekend.
During the lunch interval the Ferrari driver said he'd been focusing on qualifying runs with particular attention on the twisty final sector, with one eye on Monaco next time out, and after narrowly being pipped by Jenson Button in the morning session with the McLaren on super-softs he dialled in the Ferrari to jump ahead.
Nico Rosberg, focusing on longer runs, briefly displaced his fellow countryman on softs but it was Vettel who responded an hour after the break with a 1m 23.220s on the yellow-banded soft tyre.
The F1 championship leader made up for effectively missing the entire Spanish Grand Prix after his dramatic first-lap clash with Lewis Hamilton by notching up over a century of laps and ended the day less than two-tenths off Vettel.
Button failed to improve his morning time but held on to third with a healthy banking of laps in the McLaren-Honda before handing over to reserve driver Stoffel Vandoorne.
Romain Grosjean made a late dart up the timesheet in the final half an hour with the ultra-soft tyres to rise to fourth with a 1m 23.882s while continuing work with a new rear wing introduced last week.
Pascal Wehrlein also enjoyed late gains using the super-softs to take fifth and push Daniel Ricciardo down a spot by just 0.01s. Red Bull's reserve driver made the most of his debut in the Toro Rosso notching up consistent lap times and topped the mini-league of reserve drivers.
Next to follow was Alfonso Celis Jr who made a late blast on super-softs into eighth having collected a century of laps for the Force India technicians to digest.
Williams reserve driver Alex Lynn got heads turning at the start of the day running an experimental new rear wing, which would be illegal under existing regulations but will be consideration with the 2017 rule changes, with a day went data collecting.
Esteban Ocon on his F1 track debut got to grips with Renault's latest engine specification bringing up the last position, as the day passed a single reported mechanical breakdown on track.