The value of PR stored in Google’s database is likely to be based on a logarithmic scale similar to the one below:

Toolbar PR   Actual PR at Google

0  1 - 10

1  10 – 100

2  100 – 1000

3  1000 – 10,000

4  10,000 – 100,000

5  100,000 – 1,000,000

And so on…

In mathematical terms, this is called a logarithmic scale, and it complicates matters.

Simply put, the PR of your page is actually a measure of support for your page. Every page that links to your page is a vote, and the total count of all votes makes up the PR.

If you think about this for a minute, it should be clear that not all votes are equal.

A vote from an important page, is going to be worth more than a vote from an unimportant page. i.e. Links from high PR pages benefit your pages far more than links from low PR pages.

A link to a new site from a PR 5 page, could give that site a PR 4, with just one link.

However, there are a couple of snags.

1. The number of outbound links on a page, affects the PR boost your page receives.

and

2. The log scale.

See the log scale above?

A PR 3 page might have an actual PR of between 1000 and 10,000.

That means that a link from a PR 3 page could give your page a PR boost of anywhere between 1000 and 10,000 (although there is a dampening factor involved, so you never actually get the full PR). A high PR 3 link would be much more valuable than a low PR 3 link.

Let’s pretend (to help simplify this) that when one page links to another, all of the PR value is passed onto the page that is being linked to.

Lets take a low PR 3 page that has an actual PR value of 1000.

a) If that page had 1 outbound link, then all 1000 of the PR would be passed to the new page.

b) What about if there were 2 outbound links? Each page would get a 500 boost to their PR.

c) What if there were 10 links on the page? Each page would only get a 100 boost to its PR.

These three examples would provide a PR boost of 1000, 500, and 100 respectively.

What does this mean in real terms?

Well, if your page had an actual PR of 3,000 and it was linked to from a page as in example (a) above, your new PR would be 3,000 + 1000 = 4000. You would still appear to be a PR 3 in Google Toolbar. To move up to a PR 4, you would need to go above 10,000. That would take an additional 6 PR 3 links of category (a) above.

If your page had a PR of 3000, how many links would it require to move it to a PR 4 if all links were of type (b) above? And type (c)?

As you can see, it is not that easy to move from a PR 3 to a PR 4, when you are getting links from low PR sites.

If we looked at the same example, but our page is PR 2 and a real Google PR of 500, how many PR 3 links would be required to move your page to a PR 3?

Well, type (a) link above would require just one, since one of these links adds 1000 to our PR.

If we considered example (b) above, again just one link would be required, since 500 + 500 = 1000 and we get a low PR 3.

If we considered the (c) type link above, we would need 5 links to get to a PR 3.

So why the long example?

Simply to show you that it is easy to go from a PR0 to PR1.

It is a little more difficult to go from a PR1 to a PR2, and more difficult still to go from a PR2 to a PR3, and so on.

As your PR increases, it takes more and more links to further increase your PR. The easiest way to quickly boost your PR is to get links from high PR pages with few outbound links on the page.

Hopefully this has started you thinking about link exchanges.

How does this affect your link exchange process?

Finally before we leave this PR primer, there is one more thing I want you to think about.

If Google sees a PR 3 as being between actual PR 1000 and 10,000, then clearly not all PR 3 pages are of the same importance. This range increases as you move up the PR scale.

A link from a high PR 3 page, could be almost as valuable as a link from a low PR 4 page.