diff --git a/RespCoarseAlign.py b/RespCoarseAlign.py
index de42600..53275c2 100644
--- a/RespCoarseAlign.py
+++ b/RespCoarseAlign.py
@@ -732,7 +732,7 @@ class MainWindow(QMainWindow):
         self.data.Config["XX_reverse"] = reverse
         epoch_min = max(0, relate // 30 // self.data.Config["ApplyFrequency"] + 1)
         epoch_max = min(len(self.data.processed_THO) // 30 // self.data.Config["ApplyFrequency"] - 1,
-                        (len(self.data.processed_XX) - relate) // 30 // self.data.Config["ApplyFrequency"] - 1)
+                        (len(self.data.processed_XX) + relate) // 30 // self.data.Config["ApplyFrequency"] - 1)
         self.ui.spinBox_SelectEpoch.setMinimum(epoch_min)
         self.ui.spinBox_SelectEpoch.setMaximum(epoch_max)
         self.ui.spinBox_SelectEpoch.setValue(epoch_min)