docs: def make_plot(self):
          """Creates the ratio plot.
  
          """
          # sets colormap for ratio comparison plot
          cmap = getattr(cm, self.colormap)
  
          # set values of ratio comparison contour
          normval = 2.0
          num_contours = 40  # must be even
          levels = np.linspace(-normval, normval, num_contours)
          norm = colors.Normalize(-normval, normval)
  
          # find Loss/Gain contour and Ratio contour
          self.set_comparison()
          diff_out, loss_gain_contour = self.find_difference_contour()
  
          cmap.set_bad(color='white', alpha=0.001)
          # plot ratio contours
  
          sc = self.axis.contourf(self.xvals[0], self.yvals[0], diff_out,
                                  levels=levels, norm=norm,
                                  extend='both', cmap=cmap)
  
          self.colorbar.setup_colorbars(sc)
  
          # toggle line contours of orders of magnitude of ratio comparisons
          if self.order_contour_lines:
                  self.axis.contour(self.xvals[0], self.yvals[0], diff_out, np.array(
                      [-2.0, -1.0, 1.0, 2.0]), colors='black', linewidths=1.0)
  
          # plot loss gain contour
          if self.loss_gain_status is True:
              # if there is no loss/gain contours, this will produce an error,
              # so we catch the exception.
              try:
                  # make hatching
                  cs = self.axis.contourf(self.xvals[0], self.yvals[0],
                                          loss_gain_contour, levels=[-2, -0.5, 0.5, 2], colors='none',
                                          hatches=['x', None, '+'])
                  # make loss/gain contour outline
                  self.axis.contour(self.xvals[0], self.yvals[0],
                                    loss_gain_contour, 3, colors='black', linewidths=2)
  
              except ValueError:
                  pass
  
          if self.add_legend:
              loss_patch = Patch(fill=None, label='Loss', hatch='x', linestyle='--', linewidth=2)
              gain_patch = Patch(fill=None, label='Gain', hatch='+', linestyle='-', linewidth=2)
              legend = self.axis.legend(handles=[loss_patch, gain_patch], **self.legend_kwargs)
  
          return