The 'Undo' and 'Redo' options allow you to undo previous operations, or repeat operations which have been undone. This can apply to changing contours, landmarks, curves or the colour mapping used in volume rendering. But it can also apply to any of the other resources which are saved with a data file, including object or graphics controls or the location of the current 3D view or reslices. The settings feature below can be used to control which are included.
Selecting the first item on the Undo or Redo list will just undo or repeat that operation: these can also be accessed using Ctrl+Z or Ctrl+Y. Alternatively, you can undo or redo multiple operations by selecting one further down each list. However, they can only be performed sequentially, since only the difference from the previous state is stored.
The Undo Settings controls allow the enabling and disabling of Undo/Redo features. They are implemented efficiently, but nevertheless will take up additional memory and can slow things down a little (since every operation needs to be recorded). If you don't need an undo/redo option, then disabling it entirely will fix that.
The Mouse settings controls allow changes to the way the mouse buttons and cursor key presses work.
Finally, selecting 'Expert mode' suppresses some of Stradview's warnings and checks: Stradview will then just do some things without asking "Are you really sure?"
All these settings are saved in your personal configuration file ('stradview.ini') so there is no need to reset them every time you launch Stradview.