"Undo" is used to undo or step back in the work you are doing with the program. The menu tells you the last operation that you did, that can be undone. For example, if you moved an object, then use "Undo", and the object will move back to where it used to be. To undo the "Undo", use "Edit - Redo".
Ez3d provides multiple levels of Undo and Redo. That is, you can repeatedly use "Undo" and "Redo" to step backward and forward in the history of your editing session.
You can set the number of levels of undo (the maximum number of times you can go back in your editing history) using "Options - Preferences". The more the number of levels, the more you can undo, but the more memory the system needs for "remembering" your actions.
Note: From time to time, the system empties the undo stack even if it is not full. For example, after you open a new project, the operations performed in the old project cannot be undone. The undo stack also gets emptied when a modeling tool is closed.
Hint: The "Undo" and "Redo" menu items update dynamically to tell you what operation you can undo at any moment. If either item is grayed out, it means that there is nothing to be undone.
