diff --git a/fixtracks/widgets/tracks.py b/fixtracks/widgets/tracks.py
index 1c4105d..08ba270 100644
--- a/fixtracks/widgets/tracks.py
+++ b/fixtracks/widgets/tracks.py
@@ -466,6 +466,9 @@ class FixTracks(QWidget):
         if state and self._reader is not None:
             self._data.setData(self._reader.asdict)
             self._timeline.setDetectionData(self._data.data)
+            maxframes = self._data.max("frame")
+            rel_width = self._windowspinner.value / maxframes
+            self._timeline.setWindowWidth(rel_width)
             self.update()
             self._saveBtn.setEnabled(True)
 
@@ -516,7 +519,16 @@ class FixTracks(QWidget):
         self.update()
 
     def on_windowSizeChanged(self, value):
-        self._timeline.setWindowWidth(value)
+        """Reacts on the user window-width selection. Selection is done in the unit of frames.
+
+        Parameters
+        ----------
+        value : int
+            The width of the observation window in frames.
+        """
+        max_frames = self._data.max("frame")
+        rel_width = value / max_frames
+        self._timeline.setWindowWidth(rel_width)
 
     def on_detectionsSelected(self, detections):
         logging.debug("Tracks: Detections selected")