WARNING: This page is about a different car, the 2015 Audi RS 5, 2014 Audi RS 5, and 2013 Audi RS 5. 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 - 500 mm:VAS6075
And A Feeler Gauge.