Undo levels

This option allows you to set the number of undo levels. For unlimited undo, check Unlimited; otherwise, uncheck it, and enter the desired number of levels in the edit box. To disable undo, set the number of levels to zero. By default, undo is unlimited. The undo history is cleared whenever you start a new project or opening an existing one. Note that unlimited undo can consume a significant amount of memory over time.