Sync device numbers. Assume you have Devce A, B and C (which are PCs, Macs, Tablets etc) . Assume on MX Keys 1 is mapped to A, 2 to B and 3 to C. This mapping is automatically synced to MX mouse so that A is 1 on both devices B is 2 on both devices C is 3 on both devices. Then if A is switch to D, this is refected on mouse.