pr is actual page rank of your site while toolbar pr is sometimes fake pr and show you the rank out of 10.
Google only updates its tool bar pagerank indicator, otherwise known as the green bar, every 3-4 months. This means that your actual current pagerank may be higher or lower than the green bar is indicating. Pagerank is determined by a number of factors, most importantly how many other sites are linking to you (and therefore voting for you). The idea is that you give a little of your pagerank to every site you link to.
The actual PR of a site keeps changing in a very short span of time but it gets reflected in the toolbar PR only after 3 months when major PR update takes place. Hence, toolbar PR always reflects major changes and it remains constant for a longer time frame. Regards, RightMan
There is 'real' PR which you never see... and toolbar PR which you see but is not accurate. The 'real' PR is what is used by Google as one of it's 200+ ranking factors. Though it carries very little weight in their algorithm, it does have a tiny impact on your rankings. This 'real' PR is constantly being updated as they discover new links to your URL or discover pages that previously linked to your URL have dropped the link or the refering page has been de-indexed. The 'real' PR can be a huge number. The toolbar PR is a snapshot of what the 'real' PR was at some point in time. The toolbar PR is updated typically once every 3-4 months. At the time the snapshot is taken, Google maps the 'real' PR to a 1-10 scale for the toolbar PR using some logirithmic function... So if it is based on a base10 logrithm then the mapping might appear as follows: Real PR...........................Toolbar PR 1-10.................................0 11-100..............................1 101-1000...........................2 1001-10000.......................3 10001-100000...................4 100001-1000000...............5 etc. By the time Google issues the toolbar PR update, the toolbar PR is already weeks out of date.
Don't be overly concerned about Google PR. While PR plays a role in determining a site's rankings, the quality and relevance of inbound links far outweigh the actual PR. This is clearly proven in the use of directory and article submissions. Very rarely will your directory or article listings be placed on a page with any significant PR, however it's the relevance of these links that will increase your rankings, and over time, PR.