Purpose
To avoid having to keep picking the datum line when using repeated section or vertical design functions on one section.
Operation
Select the section or cross section by picking its datum line and click Yes. When this section has been set as the default it is the only one that can be worked on. To return to not having a default section set just run the menu item again but pick any entity that is not a section datum line or pick no entity. Closing the drawing will also stop the default.
