Google has its own FREE tracking feature called "Channels". Channels remind
me of spy movies, where a smart chip is planted in the arm of a super
sleuth, making it easier to track his activities or whereabouts.

AdSense hands you 50 such chips. Use them to track ads on specific domain
names or to group ads according to specific ad formats, keywords, their
location on the page etc. You can use any other factor that might impact
their effectiveness, based on the type of website you have.

Channel those clicks!
Google tells you many things about each Channel, such as the ad
impressions, click-throughs and earnings data.

You can use the channel reports to find out which channels are making you
the most money — and how to increase your earnings for other channels.