Google Datacenter Analyzer explained.
Google has several Datacenters to serve their Search Engine. Every Datacenter has it's own IP-address. These addresses are shown to you in the results of this tool. You can click on the Datacenter IP-addresses for futher research.
Your PageRank is not allways the same on every Datacenter. Every now and then Google checks all webpages in their database to find out if the PageRank is still approriate. This is not done for all the Datacenters at the same time but they change one by one.
Using this Datacenter Analyser you can see the PageRank changes take place in time. The whole process is called the Google dance.
When you see the first Datacenter change you know what your future PageRank will be in the rest of the world. It can take several weeks before all Datacenters are up to date.
This function doesn't work anymore. Google now updates the datacenters constantly, so there is no need for the datacenter analyzer.