Index: Ringtoets/Common/src/Ringtoets.Common.Data/Contribution/FailureMechanismContribution.cs
===================================================================
diff -u -r7e18d72b65e2041b1493dca3bd0b722d1fa5a664 -recf136a787efcd5d3f171f8aee8930f84a89e80a
--- Ringtoets/Common/src/Ringtoets.Common.Data/Contribution/FailureMechanismContribution.cs	(.../FailureMechanismContribution.cs)	(revision 7e18d72b65e2041b1493dca3bd0b722d1fa5a664)
+++ Ringtoets/Common/src/Ringtoets.Common.Data/Contribution/FailureMechanismContribution.cs	(.../FailureMechanismContribution.cs)	(revision ecf136a787efcd5d3f171f8aee8930f84a89e80a)
@@ -34,7 +34,7 @@
     public class FailureMechanismContribution : Observable
     {
         private readonly ICollection<FailureMechanismContributionItem> distribution = new List<FailureMechanismContributionItem>();
-        private int norm;
+        private double norm;
 
         /// <summary>
         /// Creates a new instance of <see cref="FailureMechanismContribution"/>. Values are taken from the 
@@ -44,15 +44,16 @@
         /// <param name="failureMechanisms">The <see cref="IEnumerable{T}"/> of <see cref="IFailureMechanism"/> on which to base
         /// the <see cref="FailureMechanismContribution"/>.</param>
         /// <param name="otherContribution">The collective contribution for other failure mechanisms.</param>
-        /// <param name="norm">The norm defined on a assessment section.</param>
+        /// <param name="norm">The norm defined on the assessment section.</param>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="failureMechanisms"/> is <c>null</c>.</exception>
         /// <exception cref="ArgumentException">Thrown when:
         /// <list type="bullet">
         /// <item>any of the <paramref name="failureMechanisms"/> has a value for <see cref="IFailureMechanism.Contribution"/> not in the interval [0, 100].</item>
         /// <item>the value of <paramref name="otherContribution"/> is not in the interval [0, 100]</item>
         /// </list>
         /// </exception>
-        /// <exception cref="ArgumentNullException">Thrown when <paramref name="failureMechanisms"/> is <c>null</c>.</exception>
-        public FailureMechanismContribution(IEnumerable<IFailureMechanism> failureMechanisms, double otherContribution, int norm)
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="norm"/> is not in the interval (0.0, 1.0) and is not <see cref="double.NaN"/>.</exception>
+        public FailureMechanismContribution(IEnumerable<IFailureMechanism> failureMechanisms, double otherContribution, double norm)
         {
             Norm = norm;
             UpdateContributions(failureMechanisms, otherContribution);
@@ -62,7 +63,7 @@
         /// Gets or sets the norm which has been defined on the assessment section.
         /// </summary>
         /// <exception cref="ArgumentOutOfRangeException">Thrown when the new value is lower than or equal to <c>0</c>.</exception>
-        public int Norm
+        public double Norm
         {
             get
             {