code: def delta_hv(scatterer):
      
      Z = scatterer.get_Z()
      return np.arctan2(Z[2,3] - Z[3,2], -Z[2,2] - Z[3,3])
docs: Delta_hv for the current setup.
  
      Args:
          scatterer: a Scatterer instance.
  
      Returns:
          Delta_hv [rad].