code: def airspeed_voltage(VFR_HUD, ratio=None):
      '''back-calculate the voltage the airspeed sensor must have seen'''
      import mavutil
      mav = mavutil.mavfile_global
      if ratio is None:
          ratio = 1.9936 # APM default
      if 'ARSPD_RATIO' in mav.params:
          used_ratio = mav.params['ARSPD_RATIO']
      else:
          used_ratio = ratio
      if 'ARSPD_OFFSET' in mav.params:
          offset = mav.params['ARSPD_OFFSET']
      else:
          return -1
      airspeed_pressure = (pow(VFR_HUD.airspeed,2)) / used_ratio
      raw = airspeed_pressure + offset
      SCALING_OLD_CALIBRATION = 204.8
      voltage = 5.0 * raw / 4096
      return voltagf airspeed_voltage(VFR_HUD, ratio=None):
      '''back-calculate the voltage the airspeed sensor must have seen'''
      import mavutil
      mav = mavutil.mavfile_global
      if ratio is None:
          ratio = 1.9936 # APM default
      if 'ARSPD_RATIO' in mav.params:
          used_ratio = mav.params['ARSPD_RATIO']
      else:
          used_ratio = ratio
      if 'ARSPD_OFFSET' in mav.params:
          offset = mav.params['ARSPD_OFFSET']
      else:
          return -1
      airspeed_pressure = (pow(VFR_HUD.airspeed,2)) / used_ratio
      raw = airspeed_pressure + offset
      SCALING_OLD_CALIBRATION = 204.8
      voltage = 5.0 * raw / 4096
      return voltage
docs: back-calculate the voltage the airspeed sensor must have seen