Undo/Redo commands accessed from Edit menu
To undo a geometric operation, select Undo from the 'Edit' menu (or press <Control-Z>) and similarly to redo a geometric operation, select Redo (or press <Control-R>). Because many of the geometric operations are dependent on specific model levels, you may need to undo or redo navigation operations before you get to the required geometric operation, e.g. 'Undo - Go to surface', etc.
Note that Undo/Redo applies only to geometric operations and changes to Model Data cannot be undone.