diff --git a/15_arch_details.ipynb b/15_arch_details.ipynb
index ac87199..2c86f66 100644
--- a/15_arch_details.ipynb
+++ b/15_arch_details.ipynb
@@ -350,7 +350,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Then we can create our head. A look at the encoder tells us the last layer has 512 features, so this head will need to receive `512*4`. Why 4? First we have to multiply by 2 because we have two images. Then we need a second multiplication by 2 because of our concat-pool trick. So we create the head as follows:"
+    "Then we can create our head. A look at the encoder tells us the last layer has 512 features, so this head will need to receive `512*2`. Why 2? We have to multiply by 2 because we have two images. So we create the head as follows:"
    ]
   },
   {
@@ -359,7 +359,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "head = create_head(512*4, 2, ps=0.5)"
+    "head = create_head(512*2, 2, ps=0.5)"
    ]
   },
   {
@@ -813,4 +813,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 2
-}
\ No newline at end of file
+}