If you change your mind about scheduling or removing a lesson, don't worry! FineTime keeps an internal record of all your manual timetable changes, and is able to reverse them on command.
Simply choose Edit - Undo from the menu bar, and the last manual change you made is immediately reversed. Additional Undo operations allow you to make further backward steps until the desired timetable state is reached.
After you have made a backward step by choosing Undo, it is possible to reverse that change by choosing Edit - Redo. This results in a forward step though your manual change history. Any number of Undo operations can be cancelled by the same number of Redo operations.