Index: Ringtoets/Common/src/Ringtoets.Common.Data/AssessmentSection/AssessmentSectionExtensions.cs
===================================================================
diff -u -r1e14ee40087ad0c42f889f6ee86c13bf6d7d192b -r0eddea1a45f0d9efb0a2a12e90eb99e814d1becb
--- Ringtoets/Common/src/Ringtoets.Common.Data/AssessmentSection/AssessmentSectionExtensions.cs	(.../AssessmentSectionExtensions.cs)	(revision 1e14ee40087ad0c42f889f6ee86c13bf6d7d192b)
+++ Ringtoets/Common/src/Ringtoets.Common.Data/AssessmentSection/AssessmentSectionExtensions.cs	(.../AssessmentSectionExtensions.cs)	(revision 0eddea1a45f0d9efb0a2a12e90eb99e814d1becb)
@@ -116,34 +116,40 @@
                 throw new ArgumentNullException(nameof(assessmentSection));
             }
 
-            if (!Enum.IsDefined(typeof(AssessmentSectionCategoryType), categoryType))
-            {
-                throw new InvalidEnumArgumentException(nameof(categoryType),
-                                                       (int) categoryType,
-                                                       typeof(AssessmentSectionCategoryType));
-            }
+            return GetAssessmentLevelFromCalculations(hydraulicBoundaryLocation,
+                                                      GetHydraulicBoundaryLocationCalculations(assessmentSection, categoryType));
+        }
 
-            IEnumerable<HydraulicBoundaryLocationCalculation> calculations;
-
-            switch (categoryType)
+        /// <summary>
+        /// Gets the <see cref="HydraulicBoundaryLocationCalculation"/> for a <see cref="HydraulicBoundaryLocation"/>
+        /// based on <see cref="AssessmentSectionCategoryType"/>.</summary>
+        /// <param name="assessmentSection">The assessment section to get the <see cref="HydraulicBoundaryLocationCalculation"/> from.</param>
+        /// <param name="hydraulicBoundaryLocation">The hydraulic boundary location to get the <see cref="HydraulicBoundaryLocationCalculation"/> for.</param>
+        /// <param name="categoryType">The category type to use while obtaining the <see cref="HydraulicBoundaryLocationCalculation"/>.</param>
+        /// <returns>The <see cref="HydraulicBoundaryLocationCalculation"/>, or <c>null</c> when:
+        /// <list type="bullet">
+        /// <item><paramref name="hydraulicBoundaryLocation"/> is <c>null</c>;</item>
+        /// <item><paramref name="hydraulicBoundaryLocation"/> is not part of <paramref name="assessmentSection"/>;</item>
+        /// <item><paramref name="hydraulicBoundaryLocation"/> contains no corresponding calculation.</item>
+        /// </list>
+        /// </returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="assessmentSection"/>
+        /// is <c>null</c>.</exception>
+        /// <exception cref="InvalidEnumArgumentException">Thrown when <paramref name="categoryType"/>
+        /// is an invalid <see cref="AssessmentSectionCategoryType"/>.</exception>
+        /// <exception cref="NotSupportedException">Thrown when <paramref name="categoryType"/>
+        /// is a valid but unsupported <see cref="AssessmentSectionCategoryType"/>.</exception>
+        public static HydraulicBoundaryLocationCalculation GetHydraulicBoundaryLocationCalculation(this IAssessmentSection assessmentSection,
+                                                                                                   HydraulicBoundaryLocation hydraulicBoundaryLocation,
+                                                                                                   AssessmentSectionCategoryType categoryType)
+        {
+            if (assessmentSection == null)
             {
-                case AssessmentSectionCategoryType.FactorizedSignalingNorm:
-                    calculations = assessmentSection.WaterLevelCalculationsForFactorizedSignalingNorm;
-                    break;
-                case AssessmentSectionCategoryType.SignalingNorm:
-                    calculations = assessmentSection.WaterLevelCalculationsForSignalingNorm;
-                    break;
-                case AssessmentSectionCategoryType.LowerLimitNorm:
-                    calculations = assessmentSection.WaterLevelCalculationsForLowerLimitNorm;
-                    break;
-                case AssessmentSectionCategoryType.FactorizedLowerLimitNorm:
-                    calculations = assessmentSection.WaterLevelCalculationsForFactorizedLowerLimitNorm;
-                    break;
-                default:
-                    throw new NotSupportedException();
+                throw new ArgumentNullException(nameof(assessmentSection));
             }
 
-            return GetAssessmentLevelFromCalculations(hydraulicBoundaryLocation, calculations);
+            return GetHydraulicBoundaryLocationCalculationFromCalculations(hydraulicBoundaryLocation,
+                                                                           GetHydraulicBoundaryLocationCalculations(assessmentSection, categoryType));
         }
 
         /// <summary>
@@ -196,11 +202,60 @@
             }
         }
 
+        /// <summary>
+        /// Gets the collection of <see cref="HydraulicBoundaryLocationCalculation"/> that belongs to
+        /// the given <paramref name="categoryType"/>.
+        /// </summary>
+        /// <param name="assessmentSection">The assessment section to get the calculations from.</param>
+        /// <param name="categoryType">The <see cref="AssessmentSectionCategoryType"/> used to determine which calculations to return.</param>
+        /// <returns>A collection of <see cref="HydraulicBoundaryLocationCalculation"/>.</returns>
+        /// <exception cref="InvalidEnumArgumentException">Thrown when <paramref name="categoryType"/>
+        /// is an invalid <see cref="AssessmentSectionCategoryType"/>.</exception>
+        /// <exception cref="NotSupportedException">Thrown when <paramref name="categoryType"/>
+        /// is a valid but unsupported <see cref="AssessmentSectionCategoryType"/>.</exception>
+        private static IEnumerable<HydraulicBoundaryLocationCalculation> GetHydraulicBoundaryLocationCalculations(IAssessmentSection assessmentSection,
+                                                                                                                  AssessmentSectionCategoryType categoryType)
+        {
+            if (!Enum.IsDefined(typeof(AssessmentSectionCategoryType), categoryType))
+            {
+                throw new InvalidEnumArgumentException(nameof(categoryType),
+                                                       (int) categoryType,
+                                                       typeof(AssessmentSectionCategoryType));
+            }
+
+            IEnumerable<HydraulicBoundaryLocationCalculation> calculations;
+
+            switch (categoryType)
+            {
+                case AssessmentSectionCategoryType.FactorizedSignalingNorm:
+                    calculations = assessmentSection.WaterLevelCalculationsForFactorizedSignalingNorm;
+                    break;
+                case AssessmentSectionCategoryType.SignalingNorm:
+                    calculations = assessmentSection.WaterLevelCalculationsForSignalingNorm;
+                    break;
+                case AssessmentSectionCategoryType.LowerLimitNorm:
+                    calculations = assessmentSection.WaterLevelCalculationsForLowerLimitNorm;
+                    break;
+                case AssessmentSectionCategoryType.FactorizedLowerLimitNorm:
+                    calculations = assessmentSection.WaterLevelCalculationsForFactorizedLowerLimitNorm;
+                    break;
+                default:
+                    throw new NotSupportedException();
+            }
+
+            return calculations;
+        }
+
+        private static HydraulicBoundaryLocationCalculation GetHydraulicBoundaryLocationCalculationFromCalculations(HydraulicBoundaryLocation hydraulicBoundaryLocation,
+                                                                                                                    IEnumerable<HydraulicBoundaryLocationCalculation> calculations)
+        {
+            return calculations.FirstOrDefault(c => ReferenceEquals(c.HydraulicBoundaryLocation, hydraulicBoundaryLocation));
+        }
+
         private static RoundedDouble GetAssessmentLevelFromCalculations(HydraulicBoundaryLocation hydraulicBoundaryLocation,
                                                                         IEnumerable<HydraulicBoundaryLocationCalculation> calculations)
         {
-            return calculations.FirstOrDefault(c => ReferenceEquals(c.HydraulicBoundaryLocation, hydraulicBoundaryLocation))?.Output?.Result
-                   ?? RoundedDouble.NaN;
+            return GetHydraulicBoundaryLocationCalculationFromCalculations(hydraulicBoundaryLocation, calculations)?.Output?.Result ?? RoundedDouble.NaN;
         }
     }
 }
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