Index: Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensions.cs
===================================================================
diff -u
--- Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensions.cs	(revision 0)
+++ Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensions.cs	(revision d2bccf12592be5246fc438434a8eec34f24d68ff)
@@ -0,0 +1,73 @@
+// Copyright (C) Stichting Deltares 2017. All rights reserved.
+//
+// This file is part of Ringtoets.
+//
+// Ringtoets is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using Ringtoets.Common.Data.AssessmentSection;
+using Ringtoets.Common.Data.Probability;
+
+namespace Ringtoets.GrassCoverErosionInwards.Data
+{
+    /// <summary>
+    /// Extension methods for obtaining level 2a results from output for an assessment of the 
+    /// grass cover erosion inwards failure mechanism.
+    /// </summary>
+    public static class GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensions
+    {
+        /// <summary>
+        /// Gets the value for the detailed assessment of safety per failure mechanism section as a probability.
+        /// </summary>
+        /// <param name="sectionResult">The section result to get the assessment layer 2A for.</param>
+        /// <param name="failureMechanism">The failure mechanism the calculations belong to.</param>
+        /// <param name="assessmentSection">The assessment section the calculations belong to.</param>
+        /// <returns>The calculated assessment layer 2A; or <see cref="double.NaN"/> when there are no
+        /// is no calculation assigned to the section result or the calculation is not performed.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
+        public static double GetAssessmentLayerTwoA(this GrassCoverErosionInwardsFailureMechanismSectionResult sectionResult,
+                                                    GrassCoverErosionInwardsFailureMechanism failureMechanism,
+                                                    IAssessmentSection assessmentSection)
+        {
+            if (sectionResult == null)
+            {
+                throw new ArgumentNullException(nameof(sectionResult));
+            }
+
+            if (failureMechanism == null)
+            {
+                throw new ArgumentNullException(nameof(failureMechanism));
+            }
+
+            if (assessmentSection == null)
+            {
+                throw new ArgumentNullException(nameof(assessmentSection));
+            }
+
+            if (sectionResult.Calculation == null || !sectionResult.Calculation.HasOutput)
+            {
+                return double.NaN;
+            }
+
+            ProbabilityAssessmentOutput derivedOutput = GrassCoverErosionInwardsProbabilityAssessmentOutputFactory.Create(sectionResult.Calculation.Output.OvertoppingOutput,
+                                                                                                                          failureMechanism, assessmentSection);
+
+            return derivedOutput.Probability;
+        }
+    }
+}
\ No newline at end of file
Index: Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/Ringtoets.GrassCoverErosionInwards.Data.csproj
===================================================================
diff -u -rcd75ebe8ea8ae0d361b7632af2bc7771a7a81a65 -rd2bccf12592be5246fc438434a8eec34f24d68ff
--- Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/Ringtoets.GrassCoverErosionInwards.Data.csproj	(.../Ringtoets.GrassCoverErosionInwards.Data.csproj)	(revision cd75ebe8ea8ae0d361b7632af2bc7771a7a81a65)
+++ Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/Ringtoets.GrassCoverErosionInwards.Data.csproj	(.../Ringtoets.GrassCoverErosionInwards.Data.csproj)	(revision d2bccf12592be5246fc438434a8eec34f24d68ff)
@@ -11,6 +11,7 @@
     <Reference Include="System.Core" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensions.cs" />
     <Compile Include="GrassCoverErosionInwardsProbabilityAssessmentOutputFactory.cs" />
     <Compile Include="OvertoppingOutput.cs" />
     <Compile Include="OvertoppingRateOutput.cs" />
Index: Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Forms/Views/GrassCoverErosionInwardsFailureMechanismSectionResultRow.cs
===================================================================
diff -u -rad12f4e2c4a765cc6c20e9f17ac051a99644ec44 -rd2bccf12592be5246fc438434a8eec34f24d68ff
--- Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Forms/Views/GrassCoverErosionInwardsFailureMechanismSectionResultRow.cs	(.../GrassCoverErosionInwardsFailureMechanismSectionResultRow.cs)	(revision ad12f4e2c4a765cc6c20e9f17ac051a99644ec44)
+++ Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Forms/Views/GrassCoverErosionInwardsFailureMechanismSectionResultRow.cs	(.../GrassCoverErosionInwardsFailureMechanismSectionResultRow.cs)	(revision d2bccf12592be5246fc438434a8eec34f24d68ff)
@@ -40,7 +40,8 @@
         /// the source of this row.</param>
         /// <exception cref="ArgumentNullException">Thrown when <paramref name="sectionResult"/> is
         /// <c>null</c>.</exception>
-        public GrassCoverErosionInwardsFailureMechanismSectionResultRow(GrassCoverErosionInwardsFailureMechanismSectionResult sectionResult) : base(sectionResult) {}
+        public GrassCoverErosionInwardsFailureMechanismSectionResultRow(GrassCoverErosionInwardsFailureMechanismSectionResult sectionResult) 
+            : base(sectionResult) {}
 
         /// <summary>
         /// Gets or sets the value of the tailored assessment of safety.
Index: Ringtoets/GrassCoverErosionInwards/test/Ringtoets.GrassCoverErosionInwards.Data.Test/GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensionsTest.cs
===================================================================
diff -u
--- Ringtoets/GrassCoverErosionInwards/test/Ringtoets.GrassCoverErosionInwards.Data.Test/GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensionsTest.cs	(revision 0)
+++ Ringtoets/GrassCoverErosionInwards/test/Ringtoets.GrassCoverErosionInwards.Data.Test/GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensionsTest.cs	(revision d2bccf12592be5246fc438434a8eec34f24d68ff)
@@ -0,0 +1,152 @@
+// Copyright (C) Stichting Deltares 2017. All rights reserved.
+//
+// This file is part of Ringtoets.
+//
+// Ringtoets is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using NUnit.Framework;
+using Rhino.Mocks;
+using Ringtoets.Common.Data.AssessmentSection;
+using Ringtoets.Common.Data.FailureMechanism;
+using Ringtoets.Common.Data.TestUtil;
+using Ringtoets.GrassCoverErosionInwards.Data.TestUtil;
+
+namespace Ringtoets.GrassCoverErosionInwards.Data.Test
+{
+    [TestFixture]
+    public class GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensionsTest
+    {
+        [Test]
+        public void GetAssessmentLayerTwoA_SectionResultNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            // Call
+            TestDelegate call = () => GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensions.GetAssessmentLayerTwoA(null,
+                                                                                                                                         new GrassCoverErosionInwardsFailureMechanism(),
+                                                                                                                                         assessmentSection);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("sectionResult", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_FailureMechanismNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new GrassCoverErosionInwardsFailureMechanismSectionResult(section);
+
+            // Call
+            TestDelegate call = () => failureMechanismSectionResult.GetAssessmentLayerTwoA(null, assessmentSection);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("failureMechanism", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_AssessmentSectionNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new GrassCoverErosionInwardsFailureMechanismSectionResult(section);
+
+            // Call
+            TestDelegate call = () => failureMechanismSectionResult.GetAssessmentLayerTwoA(new GrassCoverErosionInwardsFailureMechanism(), null);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("assessmentSection", exception.ParamName);
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_SectionResultWithoutCalculation_ReturnsNaN()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new GrassCoverErosionInwardsFailureMechanismSectionResult(section);
+
+            // Call
+            double assessmentLayerTwoA = failureMechanismSectionResult.GetAssessmentLayerTwoA(new GrassCoverErosionInwardsFailureMechanism(), assessmentSection);
+
+            // Assert
+            Assert.IsNaN(assessmentLayerTwoA);
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_CalculationWithoutOutput_ReturnsNaN()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new GrassCoverErosionInwardsFailureMechanismSectionResult(section);
+
+            failureMechanismSectionResult.Calculation = new GrassCoverErosionInwardsCalculation();
+
+            // Call
+            double assessmentLayerTwoA = failureMechanismSectionResult.GetAssessmentLayerTwoA(new GrassCoverErosionInwardsFailureMechanism(), assessmentSection);
+
+            // Assert
+            Assert.IsNaN(assessmentLayerTwoA);
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_CalculationWithOutput_ReturnsDerivedProbability()
+        {
+            // Setup
+            var failureMechanism = new GrassCoverErosionInwardsFailureMechanism();
+
+            var mocks = new MockRepository();
+            IAssessmentSection assessmentSection = AssessmentSectionHelper.CreateAssessmentSectionStub(failureMechanism, mocks);
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new GrassCoverErosionInwardsFailureMechanismSectionResult(section);
+
+            failureMechanismSectionResult.Calculation = new GrassCoverErosionInwardsCalculation
+            {
+                Output = new TestGrassCoverErosionInwardsOutput()
+            };
+
+            // Call
+            double assessmentLayerTwoA = failureMechanismSectionResult.GetAssessmentLayerTwoA(new GrassCoverErosionInwardsFailureMechanism(), assessmentSection);
+
+            // Assert
+            Assert.AreEqual(0.5, assessmentLayerTwoA);
+            mocks.VerifyAll();
+        }
+    }
+}
\ No newline at end of file
Index: Ringtoets/GrassCoverErosionInwards/test/Ringtoets.GrassCoverErosionInwards.Data.Test/Ringtoets.GrassCoverErosionInwards.Data.Test.csproj
===================================================================
diff -u -rcd75ebe8ea8ae0d361b7632af2bc7771a7a81a65 -rd2bccf12592be5246fc438434a8eec34f24d68ff
--- Ringtoets/GrassCoverErosionInwards/test/Ringtoets.GrassCoverErosionInwards.Data.Test/Ringtoets.GrassCoverErosionInwards.Data.Test.csproj	(.../Ringtoets.GrassCoverErosionInwards.Data.Test.csproj)	(revision cd75ebe8ea8ae0d361b7632af2bc7771a7a81a65)
+++ Ringtoets/GrassCoverErosionInwards/test/Ringtoets.GrassCoverErosionInwards.Data.Test/Ringtoets.GrassCoverErosionInwards.Data.Test.csproj	(.../Ringtoets.GrassCoverErosionInwards.Data.Test.csproj)	(revision d2bccf12592be5246fc438434a8eec34f24d68ff)
@@ -19,6 +19,7 @@
     <Reference Include="System.Core" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="GrassCoverErosionInwardsFailureMechanismSection2aAssessmentResultExtensionsTest.cs" />
     <Compile Include="GrassCoverErosionInwardsProbabilityAssessmentOutputFactoryTest.cs" />
     <Compile Include="OvertoppingOutputTest.cs" />
     <Compile Include="OvertoppingRateOutputTest.cs" />