Scene A and Scene B sliders

It’s because it is a preset style console. With an Express 24/48 in ‘2 scene mode’ you can have a Cue 1 set in the top row of 24 and the next 2 Cue in the bottom row of 24 and then cross fade between them. Then set Cue 3 in the top row. ‘A’ fader is the top and ‘B’ fader is the bottom. You can control the in and out fade separately between the 2 or move both together to do a straight cross fade. (There are other things around fader pairs but the above is the basic usage of a cross-fader pair)

Watch this: https://www.youtube.com/watch?v=FRO5YTVZ3AE