Lexmark T656 Technical Reference Manual page 41

Data will consist of an 18-digit identification code, which is composed of:
• a 2-digit post code,
• a 2-digit billing district code,
• a 6-digit customer account number, and
• an 8-digit item number.
To enhance readability, "." characters (ASCII 46) may appear anywhere in the data; they are ignored. Three "."
characters will be inserted automatically at the correct positions in the human-readable text printed with a
Swiss Postal bar code symbol, separating the four components of the identification code.
Invalid characters or lengths in the identification code will be flagged with an error.
One-dimensional bar codes
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