diff --git a/msspecbook/Activity09/Activity09.ipynb b/msspecbook/Activity09/Activity09.ipynb
index 23a6577..e72a966 100644
--- a/msspecbook/Activity09/Activity09.ipynb
+++ b/msspecbook/Activity09/Activity09.ipynb
@@ -6,6 +6,7 @@
    "id": "aa43e0e7-0c18-4750-9e2b-3a48f106d2ca",
    "metadata": {},
    "source": [
+    "(RFactor)=\n",
     "# Activity 9: Comparing simulation and experiment with R-factors\n",
     "In order to extract precise crystallographic information from electronic spectroscopy, we need to compare MsSpec calculations with experimental results and adjust the modelling parameters to simulate the experiment as accurately as possible.\n",
     "\n",