code: def altitude_diff(msg):
      
      tc = common.typecode(msg)
  
      if tc != 19:
          raise RuntimeError("%s: Not a airborne velocity message, expecting TC=19" % msg)
  
      msgbin = common.hex2bin(msg)
      sign = -1 if int(msgbin[80]) else 1
      value = common.bin2int(msgbin[81:88])
  
      if value == 0 or value == 127:
          return None
      else:
          return sign * (value - 1) * 25
docs: Decode the differece between GNSS and barometric altitude
  
      Args:
          msg (string): 28 bytes hexadecimal message string, TC=19
  
      Returns:
          int: Altitude difference in ft. Negative value indicates GNSS altitude
              below barometric altitude.