When selecting an excluded field value, previous selections in conflict with the new choice are canceled. To prevent a previous selection from getting canceled this way, it is possible to lock all the selections in a list box by opening its Object menu and choosing the Lock command.
When trying to select a value which is incompatible with a locked selection in another field, the selection will fail.
By means of the Override Locked Field setting for list boxes, multi boxes and slider objects it is possible to override a locked selection in a field from a specific sheet object. The field will still be locked for logical changes stemming from selections in other fields. This option is on by default for slider objects.