diff --git a/04-One-Dimensional-Kalman-Filters.ipynb b/04-One-Dimensional-Kalman-Filters.ipynb
index 0a646d4..c3c1898 100644
--- a/04-One-Dimensional-Kalman-Filters.ipynb
+++ b/04-One-Dimensional-Kalman-Filters.ipynb
@@ -454,7 +454,7 @@
     {
      "data": {
       "text/plain": [
-       "𝒩(μ=10.377, 𝜎²=0.037)"
+       "𝒩(μ=10.800, 𝜎²=0.008)"
       ]
      },
      "execution_count": 10,
@@ -472,7 +472,11 @@
     "    posterior = gaussian_multiply(likelihood, prior)\n",
     "    return posterior\n",
     "\n",
-    "update(pos, move)"
+    "# test the update function\n",
+    "predicted_pos = gaussian(10., .2**2)\n",
+    "measured_pos = gaussian(11., .1**2)\n",
+    "estimated_pos = update(predicted_pos, measured_pos)\n",
+    "estimated_pos"
    ]
   },
   {