(F). Supermarket's bar code, the librarian's magic wand':

A patch of black- and - white stripes - which would look like a miniature zebra crossing, were it not for the width variations of its constituent elements - appeared on some packages of consumer goods at the beginning of the decade (1980-). By now, its presence on the High Street goods is almost universal. The 'bar code ' as it is called, is also widely used by lending libraries. It takes much less time to scan the code than to read and key a price into a cash register. There is greater accuracy, too, as the item price can checked against the computer- held, daily updated value, countering labelling mistakes or abuse. Automatic, papers stock updating streamlines management. Advantages of using bar codes in other fields include increased patient safety through label checks on medicine bottles, automation in programmable package. Several codes are at present in use. The most frequently encountered is the Universal Product Code (UPC) of which five versions exist. In it , the first two decimal digits encode the country of origin ,the next five the manufacturer, and the following five the description of the item. The last one is the all important check digit. In the centre and at both extremities are pairs of easily recognisable guard bars. The beauty of the system lies in the method of decoding the information. After extensive processing it ends up as a series of electronic on/off signals. These are decoded by the ratio of the on and off duration. In addition this can be read in both the left - to right and right - to - left directions. Scanning the code: Most bar code scanners fall into two categories : the in-contact hand-held pen-like wand and the out- of-contact laser beam sweeper. The first type is suitable for light-traffic retailers, stores, libraries, computer users, etc. The second has for its major application area the mass traffic supermarket. A LED chip and a photo diode + transistor chip share a common substance.

Figure 24.: A diagram of UPC version of Bar code. User readable numerical are also present for convenience