diff --git a/src/wallitem.cpp b/src/wallitem.cpp
--- a/src/wallitem.cpp
+++ b/src/wallitem.cpp
@@ -34,6 +34,7 @@ static const std::string _module_id("$Id
 WallItem::WallItem( Wall *w, int wallnumber, QGraphicsScene *canvas )
   : QGraphicsLineItem( 0, canvas ), SimItemBase( w, canvas){
 
+  /* wn == 1 -> C1; wn == 2 -> C2. This way we can tell which cell a wallitem belongs to. */
   wn = wallnumber;
 
   extern Parameter par;