diff --git a/FreePIE.Core/Common/CurveMath.cs b/FreePIE.Core/Common/CurveMath.cs
index 172fb0fd..a8953506 100644
--- a/FreePIE.Core/Common/CurveMath.cs
+++ b/FreePIE.Core/Common/CurveMath.cs
@@ -80,6 +80,7 @@ public static double SolveCubicSpline(IList<Point> knownSamples, double z)
 
             if (np > 1)
             {
+                if (knownSamples[0].X == z) return knownSamples[0].Y; 
 
                 double[] a = new double[np];
 
@@ -182,13 +183,13 @@ public static double SolveCubicSpline(IList<Point> knownSamples, double z)
 
         private static void SolveTridiag(double[] sub, double[] diag, double[] sup, ref double[] b, int n)
         {
-            /*                  solve linear system with tridiagonal n by n matrix a
-                                using Gaussian elimination *without* pivoting
-                                where   a(i,i-1) = sub[i]  for 2<=i<=n
-                                        a(i,i)   = diag[i] for 1<=i<=n
-                                        a(i,i+1) = sup[i]  for 1<=i<=n-1
-                                (the values sub[1], sup[n] are ignored)
-                                right hand side vector b[1:n] is overwritten with solution 
+            /*                  solve linear system with tridiagonal n by n matrix a
+                                using Gaussian elimination *without* pivoting
+                                where   a(i,i-1) = sub[i]  for 2<=i<=n
+                                        a(i,i)   = diag[i] for 1<=i<=n
+                                        a(i,i+1) = sup[i]  for 1<=i<=n-1
+                                (the values sub[1], sup[n] are ignored)
+                                right hand side vector b[1:n] is overwritten with solution 
                                 NOTE: 1...n is used in all arrays, 0 is unused */
             int i;
             /*                  factorization and forward substitution */