From Inside AdSense, Google announces that it is now possible to assign multiple custom channels to a single ad unit. These custom channels will reside under main channels as I understand it. This new feature enables publishers to track ad performance with greater flexibility and view more granular information. When generating ad code, AdSense publishers will be able to add up to 5 custom channels to a specific instance of ad code.

Okay so what are the benefits? Google explains that multiple channels can be very useful when you want to track one ad unit across several different metrics simultaneously. They give an example of a sports site where you've placed a leaderboard AdSense ad at the top and bottom of every page. In tracking performance of the ad placement, you create two custom channels, "TopLeaderboard" and "BottomLeaderboard" which I then assume will allow you to see which ad performs better.



They remind us that ad units tagged with multiple custom channels will log impressions or clicks in each main channel. As a result, you'll see a higher number of impressions and clicks when you view your channel reports than when you view your aggregate reports.