Williams head of vehicle performance Rob Smedley reckons that the pecking order across the next couple of races will indicate the form book for the remainder of the season.
Williams has enjoyed a revival after a dismal 2013 season as they sit in sixth place in the championship with 36 points.
"Spain is a good leveller," said Smedley. "Getting back to Europe gives teams the opportunity to bring further upgrades,which we will also be doing. Barcelona and the following two or three races gives everyone a good indication of how the rest of the season will play out and who has made the most progress since the start of the season.
"The teams and drivers know the track well, meaning we can gain a lot of accurate data on how the upgrades are working. This knowledge is also very useful when back in factory; it means we can replicate the track and conditions very closely.
"The track itself has a very good mix of long straights, some high speed corners like turn three and some more technical and slower sections.Turn three is important for managing tyre wear so it's something engineers and drivers have to monitor throughout the weekend. We feel prepared going in to the weekend and are now interested to see where we are in comparison to our competitors."
Felipe Massa echoed comments made by Smedley.
"Downforce is really important in Spain so we have to make sure the aerodynamic set-up is correct," he said. "We have been working on developing the car in this area. Barcelona is historically a place where teams bring upgrades, but as every team does this it's a case of whose upgrades make the most difference."