In the manual it states: "At the top of the Radio tab you’ll also see a pressure setting (QNH) taken from the nearest airfield with a recent METAR bulletin."

Presumably if I'm flying low enough to get a mobile signal then this will be updated (yes have a cellular iPad).

However, if above say 5,000' in Wales, does SD keep a record of airfields on my route and populate the QNH field as I go along but with data that will only be relevant at the time of last contact with the mobile phone network? Agreed QNH shouldn't change massively during a flight but just curious.