well, it is funny you should say that you dont know what it does - considering you have seen the raw code from the ECU's

if in fact ECU-MAN is correct (i dont see why he wouldnt be, i simply had heard Honda decided not to use BARO sensors in Aust. due to lack of any mountains) and Aussie Hondas do have the BARO sensor then the ECU's do actually *compare* the outside air to the MAP signal and use this as an altitude correction function in determining injector PW's...

so for your info - the BARO does not function as a back up to the MAP sensor - how could it? it is not even connected to the intake manifold...

and it is exactly the same as the MAP sensor in its reference voltages as it is the same type of sensor.