Former world champion Jenson Button pointed to 'positive progress' at McLaren-Mercedes after setting the second-quickest lap time on the opening day of the final pre-season F1 2011 group test in Barcelona - almost a second faster than the team's benchmark with the new MP4-26 around the Circuit de Catalunya last week, and more than two seconds clear of his own previous best effort.

Button spent the morning evaluating a number of new parts - including a new-for-2011 front-wing - as well as conducting pit-stop practice and studies with the full race-crew, followed by longer runs and tyre analysis in the afternoon.

There was also a rather distinctive and extreme-looking, porpoise-shaped measuring device fitted to the nosecone of the British star's car. It is believed that the addition was designed to accurately measure front wing 'flex' - an area in which McLaren notably trailed arch-rivals Red Bull Racing and Ferrari in F1 2010 - but the team confirmed that the radical and bulbous appendage was for testing and long-term development purposes only and will not be raced.

"The last couple of tests haven't been perfect for us, and I think that's partly due to us lacking set-up work, but today I think we made some positive progress with the MP4-26's balance," revealed Button, who wound up behind only Red Bull's Mark Webber on the final timesheets following 74 laps on what was a cold winter's day threatened constantly by rain. "This morning, I did a number of short runs and, in the afternoon, we did some long runs, looked at set-up and balance and spent the rest of the day looking at tyre consistency.

"I know there's not much testing left - I only have one more day in the car - but, after today, I feel we can make further positive progress over the next few days. Given the limited amount of set-up work we've completed this winter, I feel we now have a good base upon which we can build - and that's nice to see."

The 31-year-old's last day in the car ahead of the Melbourne curtain-raiser at the end of the month will come on Friday, with team-mate, compatriot and title-winning predecessor Lewis Hamilton taking to the wheel on Wednesday and Saturday as McLaren splits the second Barcelona test into a brace of separate two-day outings, with a changeover day on Thursday to facilitate the arrival of new components for the car.

To see Tuesday's testing times, click here