Many items here, googles Rankings are now almost fluid, they no longer update on a daily or weekly basis, each time you click you can get a different result. Secondly datacenters have different results as well so you can see variations by simply pulling data from another datacenter that is behinf google.com.
The last most important item is google likes to cache your search results, so dont rely on clicking in google and getting real results unless you clear all your cache and cookies, and are also not logged into google at all.