the truth is the start/end/middle codes don't correspond to any number at all,
and furthermore, the numbers on one side of the middle are negative images. Each number will have two black and two white strips, you see, in other words four black/white transitions per digit. The middle bar has two black lines surrounded by white on either side, or five strips in total, allowing the negative patterns on the other side to follow straight on from it. Thus it can be scanned upside down and still work.
( Moon Girl Technologies horrendous beanbag, Fri 2 Dec 2011, 22:33, Reply)