diff --git a/01-ExamplesPaper1-Field-Lines.ipynb b/01-ExamplesPaper1-Field-Lines.ipynb
index f5953f3..33aaace 100644
--- a/01-ExamplesPaper1-Field-Lines.ipynb
+++ b/01-ExamplesPaper1-Field-Lines.ipynb
@@ -123,25 +123,26 @@
     "    N = 100\n",
     "    ds = float(distance) / N\n",
     "    \n",
-    "    X = np.zeros(N)\n",
-    "    Y = np.zeros(N)\n",
-    "    Z = np.zeros(N)\n",
+    "    # To create N line segments, we need N+1 points",
+    "    X = np.zeros(N+1)\n",
+    "    Y = np.zeros(N+1)\n",
+    "    Z = np.zeros(N+1)\n",
     "    \n",
     "    X[0] = x0\n",
     "    Y[0] = y0\n",
     "    Z[0] = z0\n",
     "    \n",
-    "    for i in range(1,N):\n",
-    "        [Bx,By,Bz] = myfield( X[i-1], Y[i-1], Z[i-1] ) # Evaluate the field at the previous point (i-1)\n",
+    "    for i in range(N):\n",
+    "        [Bx,By,Bz] = myfield( X[i], Y[i], Z[i] ) # Evaluate the field at the previous point i\n",
     "        # Normalise the vector:\n",
     "        magnitude = np.sqrt( Bx**2 + By**2 + Bz**2 )\n",
     "        Bnx = Bx / magnitude\n",
     "        Bny = # insert your code\n",
     "        Bnz = # insert your code\n",
-    "        # Now evaluate the field line location at the current point (i)\n",
-    "        X[i] = X[i-1] + Bnx*ds\n",
-    "        Y[i] = # insert your code\n",
-    "        Z[i] = # insert your code\n",
+    "        # Now evaluate the field line location at the current point (i+1)\n",
+    "        X[i+1] = X[i] + Bnx*ds\n",
+    "        Y[i+1] = # insert your code\n",
+    "        Z[i+1] = # insert your code\n",
     "    \n",
     "    return X, Y, Z # Return the coordinates of the field line"
    ]