diff --git a/power-stats.ipynb b/power-stats.ipynb
index 30cba32e7431cd1bb97225ebe75195b92509b5cd..82b9d2d370410893653d250d5262049007e92e18 100644
--- a/power-stats.ipynb
+++ b/power-stats.ipynb
@@ -32,6 +32,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "# https://stackoverflow.com/a/9031848\n",
     "import warnings\n",
     "warnings.filterwarnings('ignore')"
    ]