diff --git a/drawing.js b/drawing.js
index 7d107a4..baf9245 100644
--- a/drawing.js
+++ b/drawing.js
@@ -12,6 +12,7 @@ var drawing = {
 };
 
 function down(e){
+	// from http://www.quirksmode.org/js/findpos.html
 	var x = e.pageX, y = e.pageY;
 	var obj = e.target;
 	do {