There is a sequentially updated bar code appearing on the front cover of copies of New Scientist. I have tried without success to decipher these.
Bar codes consist of patterns of light and dark areas.
When a beam of light is shone at the bar code, the light areas reflect the light back to the reader while the dark areas absorb the light. Most bar code readers consist of a low-powered laser as the light source, and a sensor to detect when the laser light is reflected back. When the laser beam is passed across a bar code, the sensor detects the presence of light spaces because they reflect well, and black bars because they reflect badly. By recording the pattern of reflections which come back from the bar code, the reader can construct an image of the bar code and will then attempt to match the pattern of bars and spaces with one it recognises. Although there seem to be a variety of different bar code readers the only real difference is the way in which they move the laser beam about.