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In airline travel, how does Saturday-night stay pricing work for multi-city itineraries?
For a roundtrip booking it is pretty clear what the destination is, but less so for more complicated itineraries. I've been playing with some transatlantic trips in online booking tools and I'm not getting a clear intuitive sense for how this works (i.e. where I need to spend the Sat night to get good pricing).
I mainly fly OneWorld carriers but would be curious to learn how this works for other airlines too.
edit: In the comments there appears to be some doubt about whether Sat night stay is still a thing, but I see this sort of price graph all the time (maybe it's an international/transatlantic/OneWorld thing?):
Here is a direct copy-and-paste from britishairways.com for a booking I'm looking at right now:
"first sun after arrival at turnaround" — how do they define "turnaround" if it's a multi-city trip?