The home page of the Green Metrics Tool shows you the last 50 runs
From here you can go into the details for a specific measurement, or compare them.
Comparing is possible for different repos, different branches and different runs as long as they are on the same machine. Also different machines are supported if you compare the same repo.
Currently we do not support comparing different machines AND different repos at the same time. The tool will notifiy you if you attempt to do so :)