docs: def __init_vertical_plot(self):
          """
          set up the vertical profile plot
  
          Returns
          -------
          """
          # clear the plot if lines have already been drawn on it
          if len(self.ax2.lines) > 0:
              self.ax2.cla()
          # set up the vertical profile plot
          self.ax2.set_ylabel(self.datalabel, fontsize=self.fontsize)
          self.ax2.set_xlabel(self.spectrumlabel, fontsize=self.fontsize)
          self.ax2.set_title('vertical point profiles', fontsize=self.fontsize)
          self.ax2.set_xlim([1, self.bands])
          # plot vertical line at the slider position
          self.vline = self.ax2.axvline(self.slider.value, color='black')