15.2.3 Which barcode types must be distinguished?
There is quite a variety of formats in use. Common to all of them is their (for lay persons undistinguishable) appearance of black bars and white spaces of different widths. We differentiate between two types of barcodes: two level codes and multilevel codes.
Two level barcodes have two different widths: narrow and wide. Interleaved 2 of 5, MSI Code, Codabar, Code 39 and Extended Code 39 are examples of two level codes.
Multilevel barcodes have more than two variants of width, they may have bars and spaces that are very narrow, narrow, normal, wide and very wide, for example. Among the multilevel barcodes we count Code 11, UPC/EAN and kin, Code 128 and Code 93.