diff --git a/src/gui_qt/main/mainwindow.py b/src/gui_qt/main/mainwindow.py
index 10420ca..77bc0c2 100644
--- a/src/gui_qt/main/mainwindow.py
+++ b/src/gui_qt/main/mainwindow.py
@@ -944,7 +944,6 @@ class NMRMainWindow(QtWidgets.QMainWindow, Ui_BaseWindow):
     def extend_fit(self, sets: list):
         w = FitExtension(self)
         res = w.exec()
-        print(res)
         if res:
             p = w.values
             x = linspace(p[0], p[1], num=p[2])
diff --git a/src/gui_qt/math/evaluation.py b/src/gui_qt/math/evaluation.py
index 617e5f9..c74bf14 100644
--- a/src/gui_qt/math/evaluation.py
+++ b/src/gui_qt/math/evaluation.py
@@ -31,13 +31,36 @@ class QEvalDialog(QtWidgets.QDialog, Ui_CalcDialog):
         self.namespace_widget.set_namespace(self.namespace)
 
     def add_data(self, data):
-        self.listWidget.clear()
+        # self.listWidget.clear()
+        tmp = []
+        while self.listWidget.count():
+            tmp.append(self.listWidget.takeItem(0))
+
         for set_id, name in data:
-            item = QtWidgets.QListWidgetItem(name)
-            item.setData(QtCore.Qt.UserRole, set_id)
-            item.setFlags(item.flags() ^ QtCore.Qt.ItemIsEditable)
-            item.setCheckState(QtCore.Qt.Checked)
-            self.listWidget.addItem(item)
+
+            # search if set was used before
+            new_one = True
+            for i in range(len(tmp)):
+                w = tmp[i]
+                if w.data(QtCore.Qt.UserRole) == set_id:
+
+                    self.listWidget.addItem(w)
+                    tmp.pop(i)
+                    new_one = False
+                    break
+
+            # new set, create item
+            if new_one:
+                item = QtWidgets.QListWidgetItem(name)
+                item.setData(QtCore.Qt.UserRole, set_id)
+                item.setFlags(item.flags() ^ QtCore.Qt.ItemIsEditable)
+                item.setCheckState(QtCore.Qt.Checked)
+                self.listWidget.addItem(item)
+
+        while len(tmp):
+            # delete remaining ListWidgetItems
+            w = tmp.pop()
+            w.deleteLater()
 
     def set_graphs(self, graphs: list):
         self.graph_comboBox.clear()