diff --git a/04-One-Dimensional-Kalman-Filters.ipynb b/04-One-Dimensional-Kalman-Filters.ipynb
index 1f8f487..f851225 100644
--- a/04-One-Dimensional-Kalman-Filters.ipynb
+++ b/04-One-Dimensional-Kalman-Filters.ipynb
@@ -945,7 +945,7 @@
     "x = gaussian(0., 20.**2)  # dog's position, N(0, 20**2)\n",
     "velocity = 1\n",
     "dt = 1. # time step in seconds\n",
-    "process_model = gaussian(velocity*dt, process_var) \n",
+    "process_model = gaussian(velocity, process_var) \n",
     "  \n",
     "# simulate dog and get measurements\n",
     "dog = DogSimulation(\n",