Index: DamEngine/trunk/src/Deltares.DamEngine.Calculators.Tests/DikesDesign/SurfaceLineHeightAdapterTest.cs
===================================================================
diff -u -r971 -r1090
--- DamEngine/trunk/src/Deltares.DamEngine.Calculators.Tests/DikesDesign/SurfaceLineHeightAdapterTest.cs	(.../SurfaceLineHeightAdapterTest.cs)	(revision 971)
+++ DamEngine/trunk/src/Deltares.DamEngine.Calculators.Tests/DikesDesign/SurfaceLineHeightAdapterTest.cs	(.../SurfaceLineHeightAdapterTest.cs)	(revision 1090)
@@ -114,8 +114,8 @@
             surfaceLine.EnsurePointOfType(pointAtToePolder.X, pointAtToePolder.Z, CharacteristicPointType.DikeToeAtPolder);
             var surfaceLineAdapter = new SurfaceLineHeightAdapter(surfaceLine, location);
             var newSurfaceLine = surfaceLineAdapter.ConstructNewSurfaceLine(newDikeHeight);
-            double oldSlope = surfaceLine.TanSlopeInside();
-            double newSlope = newSurfaceLine.TanSlopeInside();
+            double oldSlope = TanSlopeInside(surfaceLine);
+            double newSlope = TanSlopeInside(newSurfaceLine);
             Assert.AreEqual(oldSlope, newSlope, cToleranceSlope);
         }
 
@@ -259,8 +259,8 @@
             var actualPoint = newSurfaceLine.CharacteristicPoints.GetGeometryPoint(CharacteristicPointType.DikeToeAtPolder);
             var expectedPoint = new GeometryPoint { X = 13 };
             Assert.IsTrue(expectedPoint.LocationEquals(actualPoint));
-            double oldSlope = surfaceLine.TanSlopeInside();
-            double newSlope = newSurfaceLine.TanSlopeInside();
+            double oldSlope = TanSlopeInside(surfaceLine);
+            double newSlope = TanSlopeInside(newSurfaceLine);
             Assert.AreEqual(oldSlope, newSlope, 0.001);
         }
 
@@ -990,5 +990,17 @@
             var newSurfaceLine = surfaceLineAdapter.ConstructNewSurfaceLine(newDikeHeight);
             Assert.Null(newSurfaceLine);
         }
+        /// <summary>
+        /// Determines the tan slope inside.
+        /// </summary>
+        /// <returns>tan slope inside</returns>
+        private static double TanSlopeInside(SurfaceLine2 line)
+        {
+            GeometryPoint dikeToeInward = line.GetDikeToeInward();
+            GeometryPoint dikeTopAtPolder = line.CharacteristicPoints.GetGeometryPoint(CharacteristicPointType.DikeTopAtPolder);
+            return (dikeTopAtPolder.Z - dikeToeInward.Z) /
+                   (dikeToeInward.X - dikeTopAtPolder.X);
+        }
+
     }
 }