How can I identify causes of a PageRank drop?

I use the Google Toolbar to monitor PageRank. I read on the Internet that it gives old and quite unreliable data. Can I have reliable realtime PageRank information about the sites I administer? And how can I identify causes of a PageRank drop? silviot, Torino, Italy Have a question? Ask it in our Webmaster Help Forum: www.google.com Want your question to be answered on a video like this? Follow us on Twitter and look for an announcement when we take new questions: twitter.com More videos: www.youtube.com Webmaster Central Blog: googlewebmastercentral.blogspot.com Webmaster Central: www.google.com