On one rotation, when the 0 mark on the damper is lined up (with the 0 mark on the timing cover), #1 is ready to fire. After the next full rotation, when the 0 mark on the damper lines up, #6 is ready to fire. And so it alternates back and forth between #1 and #6 being ready to fire after each full rotation aligns the 0 damper 0 mark with the 0 mark on the timing cover.