The undo list is a history of the changes that you have made to a workbook. It is located on the Quick Access Toolbar, and can be accessed by clicking the Undo button or pressing CTRL+Z. The undo list can be used to undo multiple changes, and can be saved so that you can continue working on your workbook at a later time.

To preserve the undo list in Excel, you need to do the following:

1. Open the workbook that you want to save.
2. Click the File tab.
3. Click Save As.
4. In the Save As dialog box, click the Tools button.
5. Click General Options.
6. In the General Options dialog box, select the Preserve Undo History check box.
7. Click OK.