Index: Core/Common/src/Core.Common.Base/Properties/Resources.Designer.cs
===================================================================
diff -u -r1119ad16afc56bb523cac630e15fb98b1fcf8d25 -rc09b65e09c7af06495433e73530b900c46414392
--- Core/Common/src/Core.Common.Base/Properties/Resources.Designer.cs	(.../Resources.Designer.cs)	(revision 1119ad16afc56bb523cac630e15fb98b1fcf8d25)
+++ Core/Common/src/Core.Common.Base/Properties/Resources.Designer.cs	(.../Resources.Designer.cs)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -152,6 +152,15 @@
         }
         
         /// <summary>
+        ///   Looks up a localized string similar to De waarde moet tussen 0 en 1 zijn..
+        /// </summary>
+        public static string PipingProbabilityAssessmentInput_A_Value_must_be_between_zero_and_one {
+            get {
+                return ResourceManager.GetString("PipingProbabilityAssessmentInput_A_Value_must_be_between_zero_and_one", resourceCulture);
+            }
+        }
+        
+        /// <summary>
         ///   Looks up a localized string similar to Vector moet 2 dimensies hebben, maar heeft er {0}..
         /// </summary>
         public static string Point2D_AddVector_Vector_must_be_2D_but_has_Dimensionality_0_ {
Index: Core/Common/src/Core.Common.Base/Properties/Resources.resx
===================================================================
diff -u -r1119ad16afc56bb523cac630e15fb98b1fcf8d25 -rc09b65e09c7af06495433e73530b900c46414392
--- Core/Common/src/Core.Common.Base/Properties/Resources.resx	(.../Resources.resx)	(revision 1119ad16afc56bb523cac630e15fb98b1fcf8d25)
+++ Core/Common/src/Core.Common.Base/Properties/Resources.resx	(.../Resources.resx)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -174,4 +174,7 @@
   <data name="RoundedDoubleConverter_ConvertFrom_String_cannot_be_empty" xml:space="preserve">
     <value>De tekst mag niet leeg zijn.</value>
   </data>
+  <data name="PipingProbabilityAssessmentInput_A_Value_must_be_between_zero_and_one" xml:space="preserve">
+    <value>De waarde moet tussen 0 en 1 zijn.</value>
+  </data>
 </root>
\ No newline at end of file
Index: Ringtoets/Piping/src/Ringtoets.Piping.Data/PipingProbabilityAssessmentInput.cs
===================================================================
diff -u -rfcc734ebbc1e5c6c02ae2dae2a184fdcb9aa4d1b -rc09b65e09c7af06495433e73530b900c46414392
--- Ringtoets/Piping/src/Ringtoets.Piping.Data/PipingProbabilityAssessmentInput.cs	(.../PipingProbabilityAssessmentInput.cs)	(revision fcc734ebbc1e5c6c02ae2dae2a184fdcb9aa4d1b)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Data/PipingProbabilityAssessmentInput.cs	(.../PipingProbabilityAssessmentInput.cs)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -19,28 +19,48 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System;
+using Core.Common.Base.Properties;
+
 namespace Ringtoets.Piping.Data
 {
     /// <summary>
     /// This class holds parameters which influence the probability estimate for a piping assessment.
     /// </summary>
     public class PipingProbabilityAssessmentInput
     {
+        private double a;
+
         /// <summary>
         /// Creates a new instance of <see cref="PipingProbabilityAssessmentInput"/>.
         /// </summary>
         public PipingProbabilityAssessmentInput()
         {
-            A = 1.0;
-            B = 350.0;
+            A = 0.4;
+            B = 300.0;
             SectionLength = double.NaN;
         }
 
         /// <summary>
         /// Gets 'a' parameter used to factor in the 'length effect' when determining the
         /// maximum tolerated probability of failure.
         /// </summary>
-        public double A { get; private set; }
+        public double A
+        {
+            get
+            {
+                return a;
+            }
+            set
+            {
+                if (!(value >= 0) || !(value <= 1))
+                {
+                    throw new ArgumentException(Resources.PipingProbabilityAssessmentInput_A_Value_must_be_between_zero_and_one);
+                }
+                
+                a = value;
+            }
+        }
 
         /// <summary>
         /// Gets 'b' parameter used to factor in the 'length effect' when determining the
Index: Ringtoets/Piping/src/Ringtoets.Piping.Forms/PropertyClasses/PipingFailureMechanismContextProperties.cs
===================================================================
diff -u -rde8e5c0dd97c9e53a07e905a0f59617e570b2259 -rc09b65e09c7af06495433e73530b900c46414392
--- Ringtoets/Piping/src/Ringtoets.Piping.Forms/PropertyClasses/PipingFailureMechanismContextProperties.cs	(.../PipingFailureMechanismContextProperties.cs)	(revision de8e5c0dd97c9e53a07e905a0f59617e570b2259)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Forms/PropertyClasses/PipingFailureMechanismContextProperties.cs	(.../PipingFailureMechanismContextProperties.cs)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -200,6 +200,11 @@
             {
                 return data.WrappedData.PipingProbabilityAssessmentInput.A;
             }
+            set
+            {
+                data.WrappedData.PipingProbabilityAssessmentInput.A = value;
+                data.WrappedData.NotifyObservers();
+            }
         }
 
         [PropertyOrder(52)]
Index: Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/PipingProbabilityAssessmentInputTest.cs
===================================================================
diff -u -rfcc734ebbc1e5c6c02ae2dae2a184fdcb9aa4d1b -rc09b65e09c7af06495433e73530b900c46414392
--- Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/PipingProbabilityAssessmentInputTest.cs	(.../PipingProbabilityAssessmentInputTest.cs)	(revision fcc734ebbc1e5c6c02ae2dae2a184fdcb9aa4d1b)
+++ Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/PipingProbabilityAssessmentInputTest.cs	(.../PipingProbabilityAssessmentInputTest.cs)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -19,6 +19,7 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System;
 using NUnit.Framework;
 
 namespace Ringtoets.Piping.Data.Test
@@ -33,10 +34,46 @@
             var pipingProbabilityAssessmentInput = new PipingProbabilityAssessmentInput();
 
             // Assert
-            Assert.AreEqual(1.0, pipingProbabilityAssessmentInput.A);
-            Assert.AreEqual(350.0, pipingProbabilityAssessmentInput.B);
+            Assert.AreEqual(0.4, pipingProbabilityAssessmentInput.A);
+            Assert.AreEqual(300, pipingProbabilityAssessmentInput.B);
 
             Assert.IsNaN(pipingProbabilityAssessmentInput.SectionLength);
         }
+
+        [Test]
+        [TestCase(-1)]
+        [TestCase(-0.1)]
+        [TestCase(1.1)]
+        [TestCase(8)]
+        public void A_InvalidValue_ThrowsArgumentException(double value)
+        {
+            // Setup
+            var pipingProbabilityAssessmentInput = new PipingProbabilityAssessmentInput();
+
+            // Call
+            TestDelegate call = () => pipingProbabilityAssessmentInput.A = value;
+
+            // Assert
+            var exception = Assert.Throws<ArgumentException>(call);
+            Assert.AreEqual("De waarde moet tussen 0 en 1 zijn.", exception.Message);
+        }
+
+        [Test]
+        [TestCase(0)]
+        [TestCase(0.1)]
+        [TestCase(1)]
+        [TestCase(0.0000001)]
+        [TestCase(0.9999999)]
+        public void A_ValidValue_SetsValue(double value)
+        {
+            // Setup
+            var pipingProbabilityAssessmentInput = new PipingProbabilityAssessmentInput();
+
+            // Call
+            pipingProbabilityAssessmentInput.A = value;
+
+            // Assert
+            Assert.AreEqual(value, pipingProbabilityAssessmentInput.A);
+        }
     }
 }
\ No newline at end of file
Index: Ringtoets/Piping/test/Ringtoets.Piping.Forms.Test/PropertyClasses/PipingFailureMechanismContextPropertiesTest.cs
===================================================================
diff -u -rde8e5c0dd97c9e53a07e905a0f59617e570b2259 -rc09b65e09c7af06495433e73530b900c46414392
--- Ringtoets/Piping/test/Ringtoets.Piping.Forms.Test/PropertyClasses/PipingFailureMechanismContextPropertiesTest.cs	(.../PipingFailureMechanismContextPropertiesTest.cs)	(revision de8e5c0dd97c9e53a07e905a0f59617e570b2259)
+++ Ringtoets/Piping/test/Ringtoets.Piping.Forms.Test/PropertyClasses/PipingFailureMechanismContextPropertiesTest.cs	(.../PipingFailureMechanismContextPropertiesTest.cs)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -1,4 +1,6 @@
-using Core.Common.Gui.PropertyBag;
+using System;
+using Core.Common.Base;
+using Core.Common.Gui.PropertyBag;
 
 using NUnit.Framework;
 using Rhino.Mocks;
@@ -15,8 +17,6 @@
         [Test]
         public void Constructor_ExpectedValues()
         {
-            // Setup
-
             // Call
             var properties = new PipingFailureMechanismContextProperties();
 
@@ -55,5 +55,63 @@
             Assert.AreEqual(failureMechanism.PipingProbabilityAssessmentInput.A, properties.A);
             Assert.AreEqual(failureMechanism.PipingProbabilityAssessmentInput.B, properties.B);
         }
+
+        [Test]
+        [TestCase(-1)]
+        [TestCase(-0.1)]
+        [TestCase(1.1)]
+        [TestCase(8)]
+        public void A_SetInvalidValue_ThrowsArgumentException(double value)
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var observerMock = mocks.StrictMock<IObserver>();
+            mocks.ReplayAll();
+
+            var failureMechanism = new PipingFailureMechanism();
+            var properties = new PipingFailureMechanismContextProperties
+            {
+                Data = new PipingFailureMechanismContext(failureMechanism, new MockRepository().StrictMock<IAssessmentSection>())
+            };
+
+            // Call
+            TestDelegate call = () => properties.A = value;
+
+            // Assert
+            var exception = Assert.Throws<ArgumentException>(call);
+            Assert.AreEqual("De waarde moet tussen 0 en 1 zijn.", exception.Message);
+            Assert.AreEqual(failureMechanism.PipingProbabilityAssessmentInput.A, properties.A);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        [TestCase(0)]
+        [TestCase(0.1)]
+        [TestCase(1)]
+        [TestCase(0.0000001)]
+        [TestCase(0.9999999)]
+        public void A_SetValidValue_SetsValueAndUpdatesObservers(double value)
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var observerMock = mocks.StrictMock<IObserver>();
+            observerMock.Expect(o => o.UpdateObserver());
+            mocks.ReplayAll();
+
+            var failureMechanism = new PipingFailureMechanism();
+            var properties = new PipingFailureMechanismContextProperties
+            {
+                Data = new PipingFailureMechanismContext(failureMechanism, new MockRepository().StrictMock<IAssessmentSection>())
+            };
+
+            failureMechanism.Attach(observerMock);
+
+            // Call
+            properties.A = value;
+
+            // Assert
+            Assert.AreEqual(value, failureMechanism.PipingProbabilityAssessmentInput.A);
+            mocks.VerifyAll();
+        }
     }
 }
\ No newline at end of file
Index: Ringtoets/Piping/test/Ringtoets.Piping.Service.Test/PipingSemiProbabilisticCalculationServiceTest.cs
===================================================================
diff -u -rcde435e88e283129f4d572fa0b9537a59baf72c2 -rc09b65e09c7af06495433e73530b900c46414392
--- Ringtoets/Piping/test/Ringtoets.Piping.Service.Test/PipingSemiProbabilisticCalculationServiceTest.cs	(.../PipingSemiProbabilisticCalculationServiceTest.cs)	(revision cde435e88e283129f4d572fa0b9537a59baf72c2)
+++ Ringtoets/Piping/test/Ringtoets.Piping.Service.Test/PipingSemiProbabilisticCalculationServiceTest.cs	(.../PipingSemiProbabilisticCalculationServiceTest.cs)	(revision c09b65e09c7af06495433e73530b900c46414392)
@@ -114,9 +114,9 @@
         }
 
         [Test]
-        [TestCase(30000, 6000, 24, 4.916313847)]
-        [TestCase(20000, 6000, 12, 4.972362935)]
-        [TestCase(20000, 8000, 24, 4.890463519)]
+        [TestCase(30000, 6000, 24, 4.777)]
+        [TestCase(20000, 6000, 12, 4.835)]
+        [TestCase(20000, 8000, 24, 4.748)]
         public void RequiredReliability_DifferentInputs_ReturnsExpectedValue(int norm, double assessmentSectionLength, double contribution, double expectedResult)
         {
             // Setup
@@ -146,7 +146,7 @@
             double fosUplift = 1.2;
             double fosHeave = 0.6;
             double fosSellmeijer = 0.9;
-            double expectedResult = 0.881;
+            double expectedResult = 0.907;
 
             var calculatorResult = new PipingOutput(double.NaN, fosUplift, double.NaN, fosHeave, double.NaN, fosSellmeijer);
             var pipingProbabilityAssessmentInput = new PipingProbabilityAssessmentInput
@@ -210,7 +210,7 @@
 
             // Assert
             RoundedDouble result = pipingCalculation.SemiProbabilisticOutput.PipingFactorOfSafety;
-            Assert.AreEqual(0.881, result, result.GetAccuracy());
+            Assert.AreEqual(0.907, result, result.GetAccuracy());
         }
 
         [Test]