From the Fingers of Henrik Flensborg Rants, Raves and Recommendations about marketing and health

AdSense ad unit tracking

Google has introduced a new feature on their Ad Performance page.

You can now differenciate between "page impressions" and "ad unit impressions".

In the old days "page impressions" were actually "ad unit impressions".

So if you had multiple ad units on one page they would look like multiple page impressions in the reports.

This has changed now.

"ad unit impressions" is exactly what it says: The number of times you have displayed an ad unit.

And "page impressions" is the number of times you have shown a page with Google AdSense ad units on.