This switches the way each volume elements are displayed. Either all faces of the elements or just the element faces on the surface of the structure are displayed. Depending on the state of ”Toggle Culling Back/Front,” either the faces pointing to the user or the faces pointing away are displayed. The default is just to show the surface pointing to the user. In the lower left corner of the drawing area,(see figure 2) a character is printed, indicating the program is in the surface mode ”s” or in the volume mode ”v”.