diff --git a/notebooks/hotair-box.ipynb b/notebooks/hotair-box.ipynb
index edc4792..be2d3cb 100644
--- a/notebooks/hotair-box.ipynb
+++ b/notebooks/hotair-box.ipynb
@@ -22,7 +22,8 @@
    },
    "source": [
     "## Hot air balloon - lift calculator\n",
-    "### Box shape\n"
+    "### Box shape\n",
+    "[Source code](https://gitea.citizen4.eu/sp9unb/balloon-calc) "
    ]
   },
   {
@@ -132,9 +133,7 @@
     "# Area\n",
     "    area = 2 * (width * height + width * depth + height * depth)\n",
     "    print( \"Area: {:.2f} [m2]\".format(area)) \n",
-    "# Coating density 300g / 4x5m = 15g/m2\n",
-    "#    coatingDensity = 15.0\n",
-    "#    print( \"Coating density: {:.2f} [g/m2]\".format(coatingDensity))     \n",
+    "# Coating density (protective film for painting): 300g / 4x5m = 15g/m2       \n",
     "    coatingWeight = coatDens * area\n",
     "    print( \"Coating weight: {:.2f} [g]\".format(coatingWeight))   \n",
     "# Lift per volume g/m3  \n",
diff --git a/notebooks/hotair-pyramid.ipynb b/notebooks/hotair-pyramid.ipynb
index 92cd63c..79e4636 100644
--- a/notebooks/hotair-pyramid.ipynb
+++ b/notebooks/hotair-pyramid.ipynb
@@ -22,7 +22,8 @@
    },
    "source": [
     "## Hot air balloon - lift calculator\n",
-    "### Inverted pyramid shape\n"
+    "### Inverted pyramid shape\n",
+    "[Source code](https://gitea.citizen4.eu/sp9unb/balloon-calc) "
    ]
   },
   {
@@ -181,9 +182,7 @@
     "# Area\n",
     "    area = surface_area(width,height,num)\n",
     "    print( \"Area: {:.2f} [m2]\".format(area)) \n",
-    "# Coating density 300g / 4x5m = 15g/m2\n",
-    "#    coatingDensity = 15.0\n",
-    "#    print( \"Coating density: {:.2f} [g/m2]\".format(coatingDensity))     \n",
+    "# Coating density (protective film for painting): 300g / 4x5m = 15g/m2   \n",
     "    coatingWeight = coatDens * area\n",
     "    print( \"Coating weight: {:.2f} [g]\".format(coatingWeight))   \n",
     "# Lift per volume g/m3  \n",