diff -r 4da9433a490d src/propagation/model/cost231-propagation-loss-model.cc
--- a/src/propagation/model/cost231-propagation-loss-model.cc	Wed Oct 12 21:14:34 2016 +0200
+++ b/src/propagation/model/cost231-propagation-loss-model.cc	Wed Oct 12 23:55:34 2016 +0200
@@ -64,13 +64,17 @@
                    "The distance under which the propagation model refuses to give results (m) ",
                    DoubleValue (0.5),
                    MakeDoubleAccessor (&Cost231PropagationLossModel::SetMinDistance, &Cost231PropagationLossModel::GetMinDistance),
+                   MakeDoubleChecker<double> ())
+    .AddAttribute ("Shadowing",
+                   "The Cm term of eq. 4.4.3 in the COST 231 final report. ",
+                   DoubleValue (3.0),
+                   MakeDoubleAccessor (&Cost231PropagationLossModel::SetShadowing, &Cost231PropagationLossModel::GetShadowing),
                    MakeDoubleChecker<double> ());
   return tid;
 }
 
 Cost231PropagationLossModel::Cost231PropagationLossModel ()
 {
-  m_shadowing = 10;
 }
 
 void
@@ -81,7 +85,7 @@
 }
 
 double
-Cost231PropagationLossModel::GetShadowing (void)
+Cost231PropagationLossModel::GetShadowing (void) const
 {
   return m_shadowing;
 }
@@ -95,7 +99,8 @@
 Cost231PropagationLossModel::SetLambda (double lambda)
 {
   m_lambda = lambda;
-  m_frequency = 300000000 / lambda;
+  const double C = 299792458;
+  m_frequency = C / lambda;
 }
 
 double
diff -r 4da9433a490d src/propagation/model/cost231-propagation-loss-model.h
--- a/src/propagation/model/cost231-propagation-loss-model.h	Wed Oct 12 21:14:34 2016 +0200
+++ b/src/propagation/model/cost231-propagation-loss-model.h	Wed Oct 12 23:55:34 2016 +0200
@@ -114,12 +114,14 @@
    */
   double GetLambda (void) const;
   /**
-   * Get the shadowing value
+   * Get the shadowing value used for the \f$ C_m \f$ term 
+   * of eq. 4.4.3 in the COST 231 final report.
    * \returns the shadowing value
    */
-  double GetShadowing (void);
+  double GetShadowing (void) const;
   /**
-   * Set the shadowing value
+   * Set the shadowing value. This value is used for the \f$ C_m \f$ term 
+   * of eq. 4.4.3 in the COST 231 final report. 
    * \param shadowing the shadowing value
    */
   void SetShadowing (double shadowing);