Rank oddity

Hi everyone,
When i search on google.com for my keyword on my PC i appear 6th on page one, however when i checked on my mac i was on page 2, then a quick check back on the pc and my position had changed again and the title had change to an old one from a couple of days back.
Has any one else spotted these oddities? what is the convention for ranking a site? can google rank a site higher just because on one machine you have looked for it more often, in which case how can you ever benchmark the site position?
Any help greatly appreciated as its driving me crazy!

They're showing ranks from different datacentres, simple as.

Should stablise soon and show the same thing.

Also if you have a google account on one machine and are logged in, that can affect the results

So if im sat in London using google, can my results come from a different data centre each time I search? or do they divide there data centers regionally... of is that one of those questions only google know?
Thanks for the replay BTW!
Is there standard best practice way to rank a site for keyword or it just going to google typing in as good as any other way?

going to google and typing it works. The other way is going through the webmaster tools which will give you an overall of your "global" ranking.

For the record, we were getting different results from different machines up here in Manchester yesterday as well, so those pesky googlites are up to something in the UK.

I was under the impression that there was only the one UK data center, but I could be wrong about that

Again thanks for your replys. I dont suppose you have any links to useful information on this?

I think you just need to follow what the data center telling you! Most SERP changes time to time specially when there is an update or google dance.

Not sure the google dance happens any more or major updates....it's more a state of constant flux

how the heck do you manage clients (or a boss) who you have told are now appearing at one postion but when they look they are appearing at another position, and another, and another! sounds like real pain in the behind.

So do people think google try and make it as hard as possible for SEO's otherwise if everyone can consistanlty influence their results thier search engine become less usfull as a search engine and people start using PPC less and less which reduces thier profits.

When algorithm tweaks are made the data centers do jump around quite a bit. I notice this alot. Thats why when you compare your SERPs its important to note what data center they come from.

As you sa a different SERP - due to the cahced version you will definately have been seeing different data center results.

One thing to note is that if you are logged into your Google account on one machine and not on another you may well see different results.

Here is a list of Known Google Data Centers.

Sorry if this is a realy stupid question but how do you find out what data centre you are getting your result from? and how can you make sure you always use the same one for reporting?
Thanks.

Edit: just looked at your link (thanks) do you know which if any of these would be a google (UK) centre as i was wanting to report on google.com and google.co.uk rankings.