diff --git a/Bowerbird/CurveOnSurface/CurveOnSurface.cs b/Bowerbird/CurveOnSurface/CurveOnSurface.cs
index b959179..93284f9 100644
--- a/Bowerbird/CurveOnSurface/CurveOnSurface.cs
+++ b/Bowerbird/CurveOnSurface/CurveOnSurface.cs
@@ -239,5 +239,22 @@ public IOrientableCurve Morph(SpaceMorph xmorph)
             xmorph.Morph(surface);
             return Create(surface, Curve);
         }
+
+        public double Ds(double t)
+        {
+            var uv = Curve.DerivativeAt(t, 2);
+            var u = uv[0].X;
+            var v = uv[0].Y;
+            var u1 = uv[1].X;
+            var v1 = uv[1].Y;
+
+            Surface.Evaluate(u, v, 1, out var _, out var xyz);
+            var s10 = xyz[0];
+            var s01 = xyz[1];
+
+            var x1 = u1 * s10 + v1 * s01;
+
+            return x1.Length;
+        }
     }
 }
diff --git a/Bowerbird/CurveOnSurface/IOrientableCurve.cs b/Bowerbird/CurveOnSurface/IOrientableCurve.cs
index 12f6c6c..9651c41 100644
--- a/Bowerbird/CurveOnSurface/IOrientableCurve.cs
+++ b/Bowerbird/CurveOnSurface/IOrientableCurve.cs
@@ -10,6 +10,8 @@ public interface IOrientableCurve
 
         Vector3d TangentAt(double t);
 
+        double Ds(double t);
+
         Vector3d NormalAt(double t);
 
         Vector3d BinormalAt(double t);
diff --git a/Bowerbird/CurveOnSurface/IntegrateComponent.cs b/Bowerbird/CurveOnSurface/IntegrateComponent.cs
index 75764d3..170e2b5 100644
--- a/Bowerbird/CurveOnSurface/IntegrateComponent.cs
+++ b/Bowerbird/CurveOnSurface/IntegrateComponent.cs
@@ -39,11 +39,11 @@ Func<double, double> Evaluate(IOrientableCurve curve, bool squared)
                 switch (ValueType)
                 {
                     case ValueTypes.NormalCurvature:
-                        return o => curve.NormalCurvatureAt(o).Length;
+                        return o => curve.NormalCurvatureAt(o).Length * curve.Ds(o);
                     case ValueTypes.GeodesicCurvature:
-                        return o => curve.GeodesicCurvatureAt(o).Length;
+                        return o => curve.GeodesicCurvatureAt(o).Length * curve.Ds(o);
                     case ValueTypes.GeodesicTorsion:
-                        return o => curve.GeodesicTorsionAt(o).Length;
+                        return o => curve.GeodesicTorsionAt(o).Length * curve.Ds(o);
                     default:
                         throw new Exception();
                 }
@@ -53,11 +53,11 @@ Func<double, double> Evaluate(IOrientableCurve curve, bool squared)
                 switch (ValueType)
                 {
                     case ValueTypes.NormalCurvature:
-                        return o => curve.NormalCurvatureAt(o).SquareLength;
+                        return o => curve.NormalCurvatureAt(o).SquareLength * curve.Ds(o);
                     case ValueTypes.GeodesicCurvature:
-                        return o => curve.GeodesicCurvatureAt(o).SquareLength;
+                        return o => curve.GeodesicCurvatureAt(o).SquareLength * curve.Ds(o);
                     case ValueTypes.GeodesicTorsion:
-                        return o => curve.GeodesicTorsionAt(o).SquareLength;
+                        return o => curve.GeodesicTorsionAt(o).SquareLength * curve.Ds(o);
                     default:
                         throw new Exception();
                 }
diff --git a/Bowerbird/CurveOnSurface/ZeroTwistingCurve.cs b/Bowerbird/CurveOnSurface/ZeroTwistingCurve.cs
index 5ff9ba6..9192f0d 100644
--- a/Bowerbird/CurveOnSurface/ZeroTwistingCurve.cs
+++ b/Bowerbird/CurveOnSurface/ZeroTwistingCurve.cs
@@ -190,5 +190,10 @@ public IOrientableCurve Morph(SpaceMorph xmorph)
             xmorph.Morph(curve);
             return Create(curve);
         }
+
+        public double Ds(double t)
+        {
+            return Curve.DerivativeAt(t, 1)[1].Length;
+        }
     }
 }