The (well-hidden) "Limits" widget is a very cool bit of visual / visceral UI design. Click the "scatter graph" button next to the Duration field and you get a

The (well-hidden) "Limits" widget is a very cool bit of visual / visceral UI design. Click the "scatter graph" button next to the Duration field and you get a scatter plot of duration against price for all the flights - which is useful data in itself - then you can drag a boundary around to set the maximum duration or price.