title: Secondary axis for Holoviews(Bokeh) graph
body: <p>I am trying to plot a set of graphs overlaid with a plot showing the % difference between them. </p>
  
  <p>The code I have for plotting:</p>
  
  <pre><code>%%output size = 200
  %%opts Curve[height=200, width=400,show_grid=True,tools=['hover','box_select'], xrotation=90]
  %%opts Curve(line_width=1)
  
  
  from bokeh.models import Range1d, LinearAxis
  
  new_df = new_df.astype('float')
  percent_diff_df = percent_diff_df.astype('float')
  
  def twinx(plot, element):
      # Setting the second y axis range name and range
      start, end = (element.range(1))
      label = element.dimensions()[1].pprint_label
      plot.state.extra_y_ranges = {"foo": Range1d(start=0, end=150)}
      # Adding the second axis to the plot. 
      linaxis = LinearAxis(axis_label='% Difference', y_range_name='foo')
      plot.state.add_layout(linaxis, 'right')
  
  wavelength = hv.Dimension('wavelength', label = 'Wavelength', unit = 'nm')
  radiance = hv.Dimension('radiance', label = 'Radiance', unit = 'W/m^2/sr/nm')
  curve = hv.Curve((new_df['Wave'], new_df['Level_9']), wavelength, radiance,label = 'Level_9', group = 'Requirements')*\
      hv.Curve((new_df['gcal_wave'],new_df['gcal_9']),wavelength, radiance,label = 'GCAL_9', group = 'Requirements')
  curve2 = hv.Curve((percent_diff_df['pdiff_wave'],percent_diff_df['pdiff_9']), label = '% Difference', group = 'Percentage Difference').opts(plot=dict(finalize_hooks=[twinx]), style=dict(color='purple'))
  curve * curve2
  </code></pre>
  
  <p>The result looks like this:
  <a href="https://i.stack.imgur.com/rMUsF.png" rel="noreferrer"><img src="https://i.stack.imgur.com/rMUsF.png" alt="enter image description here"></a></p>
  
  <p>The flat blue graphs are actually supposed to look like this:
  <a href="https://i.stack.imgur.com/ouIw1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ouIw1.png" alt="enter image description here"></a></p>
  
  <p>I need to plot the two graphs on two scales. I seem to be able to add a scale but not attach any of the plots to the scale.</p>