1. Undo
Reverts the listed operation. This may affect graphics parameters and device settings, which could trigger additional effects (like graphcis/sweep reset). Not all operations can be undone, so please check that the listed operation is really what you want to be undone.
2. Redo
Reverts the last Undo action, restoring the previous state.
3. Clean Undo Stack
Discards all stored Undo commands, see Undo / Redo Control for more details on this.