I find many tools which can get PageRank, but some of them indicate different number.

the command "pagerank" in google doesn't work for my page (PR5 from other tools), which says "don't know the link".

I am wondering which tool is authority one? how to use it?
why google doesn't know my page's rank with "pagerank" command?

BTW, I often use the one in www.seochat.com

Pagerank can be different depending on which google server returns the answer ;) I have noticed from your other threads that you really are worried about your pagerank. There is no 1 right pagerank, but generally they are not that far off from one another.

The tool I oftne use is: http://www.prchecker.info/check_page_rank.php

I have noticed from your other threads that you really are worried about your pagerank. ...
I tell you truth: I even didn't know the word "PageRank" before I came here this or last month.

My pages' rank increse a little now ...

why google command "pagerank" doesn't know a page of PR5 evaluated by tool from www.seochat.com?

I use
http://www.seologs.com/pr-dc-check.html

could you PM me the link to your site?
it seems to me a very interesting phenomenon

...why google command "pagerank" doesn't know a page of PR5 evaluated by tool from www.seochat.com?

Pagerank isn't a "google command". The proper pagerank for a site will come from the google toolbar itself. If you don't have one installed, sites running a proper script will generally give a correct answer. There's a different between a pagerank script and a pagerank prediction script.

The PR script on www.syndac.com/pagerank.php will always give the current PR, which should match the toolbar. It always has for me.

I'm not sure what you mean by "pagerank command," but if you mean that the way you can type link:example.com to get the listed backlinks for that domain, you're trying pagerank:example.com, like Amdac says there is no such command.

He's also right that of course Google is the best "authority" on PageRank. And third party tools are getting the score from Google. But here's the catch: Google at times makes different numbers available from various data centers at the same time. The happens as a PageRank refresh is happening, as the new data rolls out to the various data centers. It happened during the recent "Big Daddy" infrastructure change because the data centers that had switched over actually had a different index and were showing the related PageRank. It's still happening as the Big Daddy shakeout continues.

So if you have a PageRank obsession you probably want one of the tools that queries a number of different data centers. That way you can obsessively worry about the different numbers that you might see sometimes, and which one will end up lasting. ;)

BTW, "PageRank prediction" or "live PageRank" tools that were using XML data meant for the Google Appliance to get the number they were using for that no longer work... Google has stopped sending a valid "RK" element among that data. So at least that simplifies the situation.

(For an explanation of the difference between "toolbar PageRank" and "live PageRank" see this post (http://www.webhostingtalk.com/showpost.php?p=3753423&postcount=9).