Barcode POSTNET

The POSTNET Barcode format allows coding only numbers. It generally contains the ZIP postal code (5 digits) and sometimes 4 additional digits (ZIP+4) for the Delivery point (DP) which corresponds to an even more precise mail collection point.

Each digit is coded in 5 bits, represented by short or long bars. The POSTNET correspondence table is:

A complete POSTNET barcode begins and ends with a bit 1 (long line), it also includes a check digit before the final 1.

The decryption of the POSTNET Code consists of reading binary short (= 0) and long (= 1) bands and then translating them via the coding table.

Example: A message 1 00011 00101 00110 1 translates to 123

POSTNET checksum is missing in this example

The POSTNET code uses a basic checksum: add all the digits and keep the digit of units $ N $. The checksum is $ 10 - N \mod 10 $.

Example: The number 678 has for sum of digits $ 6+7+8 = 21 $, the unit digit is $ 1 $. The checksum is $ 10 - 1 = 9 $.

The POSTNET barcode has a graphic form made up of long and short lines.

The POSTNET barcode has a variable length.

The POSTNET barcode begins and ends with a long line.

The binary reading of the POSTNET barcode has a length equal to 2 modulo 5 (because 2 bits 1 are added both the beginning and at the end and the remaining characters are on 5 bits).