code: def add_chan_labels(self):
          
          window_start = self.parent.value('window_start')
          window_length = self.parent.value('window_length')
          label_width = window_length * self.parent.value('label_ratio')
  
          for row, one_label_item in enumerate(self.idx_label):
              self.scene.addItem(one_label_item)
              one_label_item.setPos(window_start - label_width,
                                    self.parent.value('y_distance') * row +
                                    self.parent.value('y_distance') / 2)
docs: Add channel labels on the left.