Undo Options

The Undo system can be enabled, disabled and configured in several ways. To open the Undo Options dialog, choose Tools -> Options...  from the main menu.

Store undo information on registry chagnes
Keep this box checked if you want undo information to be stored on registry changes so that you can undo them later. Only if this box is checked, registry changes will be tracked so they can be undone.

Display actions that have been undone
If this box is checked then registry changes which are listed in the Undo view will remain visible after they have been undone, so that you have the possibility to redo the action.

If undo cannot take place because the key or value has een changed after the action, propose to restore to the original situation instead
Actions that are listed in the undo window may not be in a state in which they can be immediately undone if other changes have been made to the affected key or value. For instance, if an existing value is changed and after changed another time there will be multiple actions that will be listed. Normally, only the last change to the value can be undone because the current contents of the value will be checked to see if it matches with the situation after the action took place. However, if you select this box, you have also the possiblity to immediately restore to the situation before you first changed the value without having to individually undo all operations. This can especially be useful to force an undo when other applications have been writing to the registry (of which no undo information is recorded at all).

Automatically delete undo information if action is older than ... hours.  
All registry changes performed with this program are being tracked. But as your registry gets edited and changed by other programs older recorded actions become obsolete as they cannot be undone anymore. Checking this box will ensure that only recent undo information will be available. It also prevents your registry from growing too big.

Delete Undo History Now
Pressing this button will clear the entire undo history ensuring no registry space is wasted on this.