Below is an example of one of the most common 1-D barcode types, the Universal Product Code (UPC). For this 1-D linear barcode, each number digit is 7 modules wide. Many people think only the black modules carry data. In fact, there are both black modules and white modules that make up this code. All of the barcode modules carry data.
The thinnest bar equals one module. Therefore, single modules are one module wide, double modules are two modules wide, triple thick modules are 3 modules wide and quadruple modules are four modules wide. The Narrow Bar Width is the size of the smallest bar in the code. The other bars in the code are based on a ratio of the narrowest bar. The Wide Bar to Narrow Bar ratio are typically 2:1, 3:1, 2.5:1.
The 1-D linear barcode Quiet Zone is the space at both the beginning and end of a code. 1-D linear barcodes must have a Quiet Zone in order to be decoded correctly.
The Guard Pattern can also be referred to as the Start and Stop Pattern. This will tell a barcode reader where the code begins and ends. Not all barcodes have this feature.
The diagram below outlines the different features and linear symbol terminology. The diagram key is below.