Jenson Button concedes McLaren yet to get a complete handle on their MP4-28 car

Jenson Button admits McLaren still have to work out how to consistently get the best out of their new MP4-28 - although doesn't yet think there is a standout 2013 car in the field.

Asked if he therefore thought the team were behind where they thought that would be after seven days of testing, Button replied: "In terms of laps completed and the testing that I have achieved, yes, I think we're behind on that. And a lot of it has been because we've been doing certain tests that have taken a bit longer than we wanted and as soon as one change takes longer it rolls into the next change and then it's lunchtime. So most of our testing is done in the afternoon these days! "So it's not been perfect and we know we've got a lot of work to do in terms of spending more time out on the circuit and understanding the car." McLaren's attempts to complete more mileage on the final day of the first Barcelona test appear likely to be hindered by rain on Friday and Button added: "It's going to be wet tomorrow so it is going to be tricky, and for me, I don't feel that I have had enough laps in the car and I think it is the same for Checo as well," he told Sky Sports News. "I am really looking forward to a good test next week in Barcelona as I don't feel that we have been able to do enough to really understand the car and where we are with the car." Despite ending the 2012 season with back-to-back wins in Austin and Brazil, McLaren's decision to introduce more revolutionary elements on the car relative to most of their rivals has been made in a bid to increase the development potential of the MP4-28. Button acknowledged even an evolutionary version of the MP4-27 would probably have been quick come Melbourne, but insists McLaren will deride longer-term gains from their decision to change concepts for 2013. "It's a very interesting season 2013, obviously with minimal regulation changes, because if we started this year with the [MP4-]27 - last year's car - with a few changes to it and developed that car through 2013, I think we could start with a very good car at the first race. "Whether it would be better than the 28 I don't know but I think it would be a very strong car. But I think after two or three races you would realise you are at the end of the development curve. For us it was important to change the development of the car so we could see a new direction in terms of development throughout the year. And it's a long season - 19 races - it';s about being strong over the whole season and not just the first couple of races. "I am still hoping we are competitive in Melbourne, it's a circuit I love and we have been competitive before the last few years. So I hope we're strong there, but there's a possibility that teams that kept the same car as last year and just developed it could also be strong." The 33-year-old did, however, stress that he didn't currently see one car that looked clearly ahead of the field. "Different cars are quick at different times and it depends on what tyre you use, and how much fuel you use. I don't think there is one standout team, or two standout teams, at the moment," he added. "There might be at the first race but at the moment there's no one that stands out to me in being superior."