diff -r 8da49ff273e0 -r 4ae2247a59f4 src/js/widgets/arrowWidget.js
--- a/src/js/widgets/arrowWidget.js	Tue Apr 03 20:30:12 2012 +0200
+++ b/src/js/widgets/arrowWidget.js	Fri Apr 06 16:49:32 2012 +0200
@@ -43,7 +43,7 @@
     var begin = (+ currentAnnotation.begin) / 1000;
     var end = (+ currentAnnotation.end) / 1000;
 
-    var duration = this._serializer.getDuration() / 1000;
+    var duration = this.getDuration() / 1000;
     var middle_time = (begin + end) / 2;
     var percents = middle_time / duration;