Backintime app and compare the difference in backups

After changing my main OS from OpenIndiana to Fedora Linux ( suspend and resume works now, most of the time -> Only when suspending in dual monitor from docking station, although just the Notebook display was active  - a resume didn't get me the X11 back. Maybe it depends although on the
network ).

I had to search for a new backup tool. In OpenIndiana I used the ZFS autosnapshot and had a lot of backups, but on Linux??

My attempt was to let a lvcreate run and create a snapshot in the
volume group. This runs as cronjob of root.

And as my users cronjob, backintime does a backup on an external USB
After creating the profile and let it run each hour, I wanted to compare the
snapshots to see the difference:

From the main window of backintime you see the button you have to select.

In the detail window you select both snapshots you like to compare and
have to push the red circled button, which was not so obvious form me.