Altitude source for flight tracking screens in the in-flight entertainment on VH-OEJ

[physicus]

Does anyone know what altitude source is used to display the flight altitude in the in-flight entertainment systems screens on VH-OEJ? I was surprised to see a rather fluctuating altitude from 6km to 11km this morning on arrival into Sydney.

[S.o.S.]

That is an interesting question physicus. You may find an quicker answer in Australia, New Zealand & the Pacific - PPRuNe Forums But do bring any answer back here for the rest of the 'cabin'.