t doesn't show sizes because it doesn't really need to.
Put the A4 paper in the feeder, select the tray with A3, set reduce/enlarge to Auto
It will enlarge to fit. Instead of showing pictures of the redundant steps that Connectkey products do, it just takes the input and compares it to the output size to figure out the size. Which is fine most of the time, the only benefit Connetckey/AltaLink had was that when you selected a reduce enlarge option it showed the percentage, and from that you could finesse it later by increasing/decreasing the percentage by a few percent if desired.