Minecraft wiki entry for Memory, associated text: There are many ways to build a T flip-flop, ranging from torches and dust through pistons to more exotic devices. Many designs depend on a quirk in sticky-piston behavior, namely that after pushing a block, a sticky piston will let go of it if the activating pulse was 1 tick or less. This allows short pulses to toggle the position of a block, which is very useful here.