To make changes in all design topics except usage, you must enter "edit mode." In edit mode, you cannot switch topics or steps, and calculations for the changes made are displayed only after you save and exit edit mode.
In edit mode, you can undo and redo all actions taken. You can either cancel the changes and exit or save the changes and exit the edit mode. After saving and exiting edit mode, the undo and redo action history will be deleted permanently.