diff --git a/diffpose/calibration.py b/diffpose/calibration.py
index c8112cf..d3ca073 100644
--- a/diffpose/calibration.py
+++ b/diffpose/calibration.py
@@ -27,6 +27,7 @@ def __init__(
         device=None,
         dtype=torch.float32,
     ):
+        """Wrapper of pytorch3d.transforms.Transform3d with extra functionalities."""
         if device is None and (R.device == t.device):
             device = R.device
 
diff --git a/notebooks/api/02_calibration.ipynb b/notebooks/api/02_calibration.ipynb
index 0ffdd7f..148ae71 100644
--- a/notebooks/api/02_calibration.ipynb
+++ b/notebooks/api/02_calibration.ipynb
@@ -114,6 +114,7 @@
     "        device=None,\n",
     "        dtype=torch.float32,\n",
     "    ):\n",
+    "        \"\"\"Wrapper of pytorch3d.transforms.Transform3d with extra functionalities.\"\"\"\n",
     "        if device is None and (R.device == t.device):\n",
     "            device = R.device\n",
     "\n",