There is something I haven't ever fully understood regarding the baro ref.
According to the 1.34.10 p9:
ALTI DISCREPANCY
triggered when difference in Capt and FO displayed altitude exceeds 250 ft (when on QNH) and 500 ft (when on STD).
I don't know which computer monitors this discrepancies. SDACs, FWCs, ADIRUS...?
Does it have to do with the FCU channels? When one of them fails we have the BARO REF...X CHECK blue line. Does that mean that with an FCU failed the ALTI DISCREPANCY will not be triggered? Or it has nothing to do with it?
But then... Why should we be extra careful in x-checking the baro ref when losing an FCU channel?
There is not a caution for "one pilot on QNH and the other in STD", right?
Next time I am during cockpit prep I will set capt baro ref to STD and then set the FO QNH to change altitude in 250 ft and 500 ft and see what happens, and then repeat the experiment with the FO in STD and capt in QNH and both on QNH, of course.
I guess the ECAM just warns of a discrepancy, whatever the reason, which can be due to one faulty probe or system or to one incorrect QNH or one PDF in QNH and the other in STD.