Codabar is a bar code formerly used in medicine for blood products, pharmacy, libraries
and parcel services. The Codabar can represent the numeric digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9, the letters A, B, C and D and six special characters. Each character is represented by seven elements - one element in the bar code is a bar and a space - where the information
is represented only by the bars, respectively the bar width, but not by spaces. Four of the seven elements are bars, three are gaps. Since the gaps do not contain any information, the Codabar has a relatively low information density. The codabar, which has a variable length, is delimited by the start and stop characters. The letters A, B, C, and D are represented only in the start and stop characters, not in the message content. No checksum is prescribed for the Codabar.