www.youtube.com/watch?v=6jYwhO4nLxs Once every few months, Google will basically take a snapshot of the entire known URLs of their index along with their corresponding "actual" PR values. Then they run a logarithmic scaling algorithm against the precise PR to scale them to values starting from 0 to 10. They publish these "scaled" Web page Ranks as what folks generally consult with as a PR replace. It is this published "scaled" PR that is accessed and displayed by the Google toolbar utility while you browse a web page.