diff --git a/Detector/DetCRD/compact/CRD_common_v01/Beampipe_v01_02.xml b/Detector/DetCRD/compact/CRD_common_v01/Beampipe_v01_02.xml
index b5301e81f50df3f319b33d2d7b044e7567f8f019..ef58b72abe1e9d6e836043f4b03a7cfb0d2316bc 100644
--- a/Detector/DetCRD/compact/CRD_common_v01/Beampipe_v01_02.xml
+++ b/Detector/DetCRD/compact/CRD_common_v01/Beampipe_v01_02.xml
@@ -9,6 +9,7 @@
   </display>
 
   <define>
+    <!--only needed for asymetry double pipe-->
     <!--constant name="ForkAsymThickness" value="BeamPipe_Dnstream_inner_radius+BeamPipe_Cu_thickness-BeamPipe_Upstream_inner_radius"/-->
   </define>