code: def get_scale_fac(fig, fiducial_width=8, fiducial_height=7):
      
      width, height = fig.get_size_inches()
      return (width*height/(fiducial_width*fiducial_height))**0.5
docs: Gets a factor to scale fonts by for the given figure. The scale
      factor is relative to a figure with dimensions
      (`fiducial_width`, `fiducial_height`).