Sometimes I’ve found I’m working on a project using sections and find that the section I need hasn’t been created. I get confused because the drawing has the needed surface in it, but the section isn’t showing up in the list when I go to try to compute the materials. It usually happens when I deleted an old surface and then come want to use a new one. To sample the missing surface go into the Toolspace and right click on the Sample Line and choose the properties. Then go into the Sections Tab and press the Sample more sources… button. From the Selection Sources dialog box choose the available source and press the Add button. You can also remove all of the section from this dialog also.