Double-decker diffuser

Holes cut perpendicular to the reference plane fed a second, upper diffuser deck, expanding the volume of air the diffuser could work and substantially increasing rear downforce.

The diffuser-start rule was written in terms of what is visible in plan view. Perpendicular holes are invisible in plan view, so the rule did not catch them.

Decisive. Brawn won both championships in the team's only season.

The protest was rejected at Australia and the appeal heard on 14 April 2009, which upheld the designs as legal. The concept was then banned for 2011 by cutting maximum diffuser height from 175 mm to 125 mm.

Both 2009 championships went to a team running the device from round one.

Survived its court challenge, which makes it the strongest evidence for the register's organising thesis — adjudication tends to favour clever geometry and punish clever mechanisms.