As a scanning device is moved across the symbol, the width pattern of the bars and spaces is analyzed to extract the original encoded data. The X dimension dictates the width of all other bars and spaces, and ultimately the length of the bar code. For proper scanning, most bar codes have a quiet zone, i.e., clear space, at either end whose width is at least 10 times the bar code's X dimension.
All bar codes use special patterns at each end, called start and stop characters.
These characters identify the symbology and also enable the scanner to read the symbol bidirectionally, decoding the data in the correct order. Bar codes also often include a check digit at the end that is determined according to an algorithm based upon the preceding characters. The check digit validates that all characters have been decoded correctly. Standardization within and across industries has been, and continues to be, essential to the phenomenal growth and widespread implementation of bar code technology. Bar code standards apply to printing, scanning, and verification of bar code symbologies.