Google announced on Twitter and Google+ yesterday that they added version history to their ad platform so you can compare the performance of an ad before and after you make changes to them.
Google wrote "version history lets you see previous versions of your ads after they’ve been edited–and how they performed. Check it out by clicking the pencil icon next to an ad in the new AdWords experience."
This help document explains:
When you edit an ad, such as change the final URL, you can see the old version of the ad by looking at its version history.Version history includes the dates each version was edited, how long that version was in place for, and what changed.
The information about how long the version was in place can include review periods, or periods where the ad wasn’t showing, for example, because it was paused.
You can download a CSV report of your ad's version history.
Here is a screen shot of how it looks:
Ginny Marvin has an additional screen shot on Search Engine Land.
