Minecraft wiki entry for Transmission, associated text: Behavior (rising-edge): When the input turns on, the lower sticky piston begins to extend, causing the upper sticky piston to retract, allowing the powered redstone dust below block A to connect to the output. All of this happens instantly (in the same redstone tick), effectively allowing a rising edge to pass through the circuit with no delay. The moving block of redstone also instantly depowers the dust below it, but by the time that turns off the repeater's output, the block of redstone has arrived to continue powering the output.