public void ShowSelectedItem()
 {
     numberTextBox.Text = ToNumber(SelectedUnit).ToString();
     messageLabel.Text  = string.Format(Resources.SelectUnitsFormSelectedUnits, SelectedUnit.GetOffOnName(CustomUnits));
     if (SelectedUnit.IsAnalog())
     {
         analogUnitsListBox.SelectedIndex  = ToNumber(SelectedUnit) - 1;
         digitalUnitsListBox.SelectedIndex = -1;
     }
     else
     {
         digitalUnitsListBox.SelectedIndex = SelectedUnit - Unit.DigitalUnused;
         analogUnitsListBox.SelectedIndex  = -1;
     }
 }