diff --git a/src/channel_calibration_dialog.py b/src/channel_calibration_dialog.py
index 50da021..c45fd85 100644
--- a/src/channel_calibration_dialog.py
+++ b/src/channel_calibration_dialog.py
@@ -71,8 +71,9 @@ class ChannelCalibrationDialog(QDialog):
 
             channel_layout.addWidget(RoundedColorRectangleWidget(ch.color))
 
+        from PyQt6.QtCore import QLocale
         float_validator = CustomDoubleValidator()
-        # float_validator.setLocale("C")
+        float_validator.setLocale(QLocale(QLocale.Language.C))
 
         # Přičíst input
         add_layout = QVBoxLayout()
@@ -138,8 +139,15 @@ class ChannelCalibrationDialog(QDialog):
                 # get the current channel object of the current (duplicated dataset)
                 channel = DetektorContainer().get().get_channel_by_uuid(channel_id)
 
-                offset = float(self.add_input.text())
-                multiple = float(self.multiply_input.text())
+                try:
+                    # validate inputs
+                    offset = float(self.add_input.text().replace(',', '.'))
+                    multiple = float(self.multiply_input.text().replace(',', '.'))
+                except ValueError:
+                    WrongDataDialog()
+                    return
+                
+
                 logging.debug(f'Calibrating channel {channel.name} +{offset} x{multiple}')
 
                 if self._only_region:
@@ -178,12 +186,37 @@ class MissingChannelDialog(QDialog):
 
         self.setWindowTitle("Vyberte kanál")
         self.setModal(True)  # Set the dialog as modal (blocks main window)
-        self.resize(300, 150)
+        self.resize(400, 75)
 
         # Main layout
         main_layout = QVBoxLayout()
         self.setLayout(main_layout)
-        main_layout.addWidget(QLabel("Vyberte kanál, na kterém chcete provést kalibraci"))
+        label = QLabel("Vyberte kanál, na kterém chcete provést kalibraci")
+        label.setAlignment(Qt.AlignmentFlag.AlignCenter)
+        main_layout.addWidget(label)
+
+        cancel_button = QPushButton("OK")
+        cancel_button.clicked.connect(self.close)
+        main_layout.addWidget(cancel_button)
+
+        # Show the dialog
+        self.exec()
+
+
+class WrongDataDialog(QDialog):
+    def __init__(self):
+        super().__init__()
+
+        self.setWindowTitle("Špatná data")
+        self.setModal(True)  # Set the dialog as modal (blocks main window)
+        self.resize(400, 75)
+
+        # Main layout
+        main_layout = QVBoxLayout()
+        self.setLayout(main_layout)
+        label = QLabel("Zadaná data nejsou platná čísla.")
+        label.setAlignment(Qt.AlignmentFlag.AlignCenter)
+        main_layout.addWidget(label)
 
         cancel_button = QPushButton("OK")
         cancel_button.clicked.connect(self.close)
@@ -193,6 +226,18 @@ class MissingChannelDialog(QDialog):
         self.exec()
 
 class CustomDoubleValidator(QDoubleValidator):
+
     def validate(self, input_str, pos):
-        input_str = input_str.replace(',', '.')  # Replace ',' with '.'
-        return super().validate(input_str, pos)
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+        # Accept both comma and dot as decimal separator for validation
+        if ',' in input_str:
+            # Allow comma as intermediate state so user can type it
+            test_str = input_str.replace(',', '.')
+            state, _, _ = super().validate(test_str, pos)
+            if state == QDoubleValidator.State.Acceptable:
+                return (QDoubleValidator.State.Intermediate, input_str, pos)
+            return (QDoubleValidator.State.Intermediate, input_str, pos)
+        return super().validate(input_str, pos)
+
+    def fixup(self, input_str):
+        # Actually replace comma with dot in the QLineEdit
+        return input_str.replace(',', '.')
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