code: async def save_z(data):
      
      if not session.tip_length:
          message = "Tip length must be set before calibrating"
          status = 400
      else:
          if not feature_flags.use_protocol_api_v2():
              mount = 'Z' if session.current_mount == 'left' else 'A'
              actual_z = position(
                  mount, session.adapter)[-1]
              length_offset = pipette_config.load(
                  session.current_model, session.pipette_id).model_offset[-1]
              session.z_value = actual_z - session.tip_length + length_offset
          else:
              session.z_value = position(
                  session.current_mount, session.adapter, session.cp)[-1]
  
          message = "Saved z: {}".format(session.z_value)
          status = 200
      return web.json_response({'message': message}, status=status)
docs: Save the current Z height value for the calibration data
  
      :param data: Information obtained from a POST request.
      The content type is application/json.
      The correct packet form should be as follows:
      {
        'token': UUID token from current session start
        'command': 'save z'
      }