Modern cash registers are actually computers that are able to read a code consisting of a series of vertical bars varying in width. These are called bar codes (or barcode) and represent numbers and other symbols. The bar code is scanned by a laser beam that is sensitive to the reflections from the line along with space thickness and variation. The reader translates the reflected light into digital data that is transferred to a computer for immediate action or storage—usually both—resulting in the addition of items purchased and an immediate inventory for the store. (For more information about computers, see “Math in Computing.”)

Many store items these days are labeled with bar codes, which use lines of varying widths to indicate numbers that can be read by laser scanners.

But bar codes aren’t only for stores. They are also used to check out books from the library, identify hospital patients, and track manufacturing and shipping movements. There are even very small bar codes used in scientific research, for example, to tag and keep track of honey bees.