diff --git a/sohstationviewer/model/reftek/reftek_data/core.py b/sohstationviewer/model/reftek/reftek_data/core.py
index 79bb4b6833d888b68c081936de1870d68476fa07..42b82dd9c0266e20dcd3ec00d849d4dfcb6783e9 100644
--- a/sohstationviewer/model/reftek/reftek_data/core.py
+++ b/sohstationviewer/model/reftek/reftek_data/core.py
@@ -56,8 +56,11 @@ class DiscontinuousTrace(Trace):
         """
         if type == 'utcdatetime' or type == 'matplotlib':
             raise NotImplementedError
-        if type == 'relative':
-            return self._times - self.stats.starttime.timestamp
+        elif type == 'relative':
+            if reftime is None:
+                return self._times - self.stats.starttime.timestamp
+            else:
+                return self._times - reftime.timestamp
         elif type == 'timestamp':
             return self._times