Google dance is term that determines the time gap after which the content on the web page is up dated.
As the time changes Google up dates your content with fresh lot to serve for better Search Engine rankings in your favour. Google sends spiders to crawl on the Internet and updates the content on Google pages. Hence producing overall page rank, now when you watch your rank on the Google toolbar, you can definitely tell your updated rank. Web masters look for the formula that defines and suggests the next time when the changes will commence. There are several thousands versions and servers on net that take time to decipher the information back. Depending on the information returned, the exact time taken is traced and date is marked. You might want to know when Google visited your site the very last time. There are several data centers of Google, each are provided with the area they have to cover. With this the chances for continuous indexing is better but not guaranteed.