Bookmarks are very handy when you want to navigate away from a particular date
without losing where you were originally.
There are 10 available bookmarks and they are remembered after program exits.
Assigning a different date and time to a bookmark overwrites the previous one.
To assign a bookmark, select a time slot and press the keys: Ctrl + Shift simultaneously
with one of the numbers from 0 to 9
To return to one of the bookmarks, press Ctrl + 0...9