old_contents: 
  def parameters(accelerator_prefix):
      """Parameters to transform the particle position with respect to
      the upstream accelerator's coordinate system to local coordinates.
  
      Returns delta_rx[m] and delta_angle[rad]
      """
      if accelerator_prefix == 'TB':
          delta_rx = 0.0
          delta_angle = 0.0
      elif accelerator_prefix == 'BO':
          delta_rx = -0.03
          delta_angle = 0.0143
      elif accelerator_prefix == 'TS':
          delta_rx = -0.022
          delta_angle = -0.005
      elif accelerator_prefix == 'SI':
          delta_rx = -0.0165
          delta_angle = 0.00537
      else:
          delta_rx = None
          delta_angle = None
      return delta_rx, delta_angle
  
new_contents: 
  def parameters(accelerator_prefix):
      """Parameters to transform the particle position with respect to
      the upstream accelerator's coordinate system to local coordinates.
  
      Returns delta_rx[m] and delta_angle[rad]
      """
      if accelerator_prefix == 'TB':
          delta_rx = 0.0
          delta_angle = 0.0
      elif accelerator_prefix == 'BO':
          delta_rx = -0.03
          delta_angle = 0.0143
      elif accelerator_prefix == 'TS':
          delta_rx = -0.022
          delta_angle = -0.005
      elif accelerator_prefix == 'SI':
          delta_rx = -0.0165
          delta_angle = 0.00537
      else:
          delta_rx = None
          delta_angle = None
      # return delta_rx, delta_angle
      return 0.0,0.0
  
subject: return zeros for relative angle and position between accelerators.