Busby SEO Challenge : following the positions

In this SEO challenge, we have to position our sites on google.com...
But the question we had withe the SEO Sphere Team was "which Data Center is the reference ?".
So it's an australian one and here is the link to follow the SERP :
http://66.249.89.99/ie?q=Busby+SEO+Challenge&num=100&hl=en&as_qdr=all&btnG=Search

But these SERP are quite strange for our pages involved in the busby seo challenge.

But anyway, this DC is the reference and that's the way it goes !!