diff --git a/test/parallel-nutrients.html b/test/parallel-nutrients.html
index b07f50e77dc406c82de01f7fd8bfdb045fd362b3..7b9766029b0bbddba64b29cfec660beb93c1a5b0 100644
--- a/test/parallel-nutrients.html
+++ b/test/parallel-nutrients.html
@@ -19,6 +19,11 @@ under the License.
 -->
 
 
+<!--
+    This data and the design of this chart is copied from:
+    http://bl.ocks.org/syntagmatic/3150059
+-->
+
 <html>
     <head>
         <meta charset="utf-8">
