How do PR checkers work? [closed]

Question

How do the millions of online 'pagerank checker' tools work?

Don't get me wrong, pagerank means very little to me, I just wondered how they give you a pagerank number, given that many of them give you a different score to other tools...

Answer 1

Answered here: http://stackoverflow.com/questions/1344917/getting-google-pagerank-via-an-api-php