When you run the application for the first time, it will update its database (with information for over 150 smartphones) before you can start using it. At any point of time, you can manually update the databases from the application settings. After that, all you need to do is select the devices you want to compare and it will show you the details.
SpecCheck can be a very simple and useful application for Android devices when you want to get in-depth comparison two devices. SpecCheck
