The Undo command reverses the last operation, including selection actions and those performed on selected objects. Redo reverses the last Undo operation.
Some actions cannot be undone: for example, applying the Collapse utility or Reset Transform utility, or saving a file, which overwrites the previous version. When you know an action cannot be undone, use first. Then if you want to undo it, use Fetch. Hold and Fetch are also commands on the .
Afer you perform an action that is undoable, the Undo command on the Edit menu shows the name of the function to be undone. After you undo an action, the Redo command Edit menu shows the name of the function you can redo.
Undo and Redo are also available as buttons on the Quick Access toolbar. You can click the Undo or Redo down-arrow to display a drop-down list that shows the last operations performed. You can highlight and reverse any number of these operations in sequence with the respective Undo or Redo command. By default, there are 20 levels of Undo. You can change the number of levels with the Customize Preferences Scene Undo group.
When you create an object, the Create operation is recorded by 3ds Max and displayed next to the activated Undo command in the Edit menu. If you undo the Create operation, the Create operation appears next to the activated Redo command in the Edit menu. The Undo and Redo commands in the Edit menu are unavailable when no valid operation was performed or recorded.