WARNING: This page is about a different car, the 2012 Audi S5, 2011 Audi S5, 2010 Audi S5, 2009 Audi S5, and 2008 Audi S5. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Checking Cylinder Head At Several Locations For Distortion
Courtesy of AUDI OF AMERICA, LLC
-- Check the cylinder head at several locations for distortion using a Straight Edge - 500mm:VAS6075
and a feeler gauge.