docs: def plot_channel_sweep(proxy, start_channel):
      '''
      Parameters
      ----------
      proxy : DMFControlBoard
      start_channel : int
          Channel number from which to start a channel sweep (should be a
          multiple of 40, e.g., 0, 40, 80).
  
      Returns
      -------
      pandas.DataFrame
          See description of return of :func:`sweep_channels`.
      '''
      test_loads = TEST_LOADS.copy()
      test_loads.index += start_channel
  
      results = sweep_channels(proxy, test_loads)
      normalized_measurements = (results['measured capacitance']
                                 / results['expected capacitance'])
      fig, axis = plt.subplots(figsize=(10, 8))
      axis.bar(normalized_measurements.index - 0.3, normalized_measurements,
               width=0.6, edgecolor='none', facecolor='limegreen')
      axis.set_xlim(left=test_loads.index.min() - 0.5,
                    right=test_loads.index.max() + 0.5)
      axis.set_xlabel('channel')
      axis.set_ylabel(r'$\frac{C_{\tt{measured}}}{C_{\tt{expected}}}$',
                      fontsize=28)
      return results