A. You fold the A3 page in half and place in a specialised transparent carrier sheet (either supplied or available separately). The scanner detects the coding strip on the carrier sheet and the driver will then read both sides and seamlessly join the two sides to form a single page document of A3 dimensions.
This function works well, but due to the requirement to fold the document, it is not suitable for all purposes of A3 scanning. Some may still be better off with an A3 scanner.