Bar codes give the necessary information regarding a product to the customer as well as to the owner, such as price, category etc. It can give necessary information like inventory details, tax payments to the company management. Even though there are many type of bar codes in use at present, the internationally famous, one is Universal Product Code (UPC). In this UPC we find small black and white bars of varying thicknesses with spacing between them, printed on packages. To read this a bar code reader or bar code scanner is used. When bar code label is kept on the scanner, the laser beam inside the scanner touches the bars, the black bars absorbs the beam and the whites reflects the beam. A photo diode in the scanner converts the beam in to electrical pulses. These pulses are fed to the computer, which converts them into digital codes. This digital code, in turn, reaches the main computer to give necessary information pertaining to the product. One can cross check the correct operation of scanner by tallying with check digit code printed at the extreme right bottom comer on the label.