This symbology, derived from the RM4SCC system used by the British Royal Mail, uses a series of bars, each of which can individually have one of four possible states, to encode information used in automated sortation and delivery onto each piece of mail. Each bar can either be short and centred (known as a tracker), medium and elevated (an ascender), medium and lowered (a descender), or full height. This symbology also uses an element known as a Data Content Identifier (or DCI), which specifies what types of information are encoded into each barcode, such as postal codes, customer information, and exact delivery points. The information that goes into each barcode is obtained from the address printed on the front of the envelope it is ultimately printed on, as well as the physical dimensions of each piece of mail. This code also uses a Reed-Solomon error correction technique, so that in case a particular piece of mail is mishandled, the information encoded in the barcode can still be correctly decoded.
Four character sets are used in PostBar codes, known as "A", "N", "Z" and "B" characters. Three-bar A characters are used exclusively to encode letters, and two-bar N characters encode only digits. Three-bar Z characters can encode either letters or digits. A and N characters are typically used to encode postal codes and country codes. Z characters are used for address locators, product types, and customer and service information. B characters are one bar each, and are used to encode base-4 machine ID's for Canada Post's internal uses.
Each barcode begins and ends with an identical pair of bars, known as "start" and "stop" fields. These are made up of one ascender and one tracker. The Data Content Identifier is always the first character after the start field.
Placeholders used to detail each PostBar format below are A, N, Z and B for the character sets described above, * for the start and stop fields, # for a space character (two full-height bars followed by one tracker), and [RS-nn] for the error-correction field, where nn is the number of bars used. Bold Z's indicate DCIs.
DCI's used in domestic barcodes fall within the range of A-L.
For PostBar format D12, as described in this article and shown here, the Postal Code is encoded using fifteen bars and the 'A' and 'N' character sets. The Address Locater encodes four alphanumerics using twelve bars and the 'Z' characters set. This format also includes a space character and twelve bars for Reed-Solomon error correction for a total count of forty nine bars.
On the other hand, PostBar format D52.01, as described in Canada Post's 4-State Bar Code Handbook and shown here, encodes the Postal Code using only twelve bars and an unknown symbology. It encodes nine alphanumerics in the Address Locater field using twenty one bars and another unknown symbology. It does not include any fields for space characters, but it does include twelve bars for Reed-Solomon error correction for a total count of fifty two bars.
Most significantly these two different formats use the exact same code for their Data Content Identifier field; specifically two Full Height bars and an Ascender which corresponds to a 'B' character using the 'Z' symbology. From samples of mail being delivered by Canada Post, the D52.01 format with an unknown symbology is the implemented standard, and not format D12 as described in this article.
Postal customers who attempt to include a D12 formatted PostBar code, or any other PostBar format or symbology as described in this article may find it is misinterpreted by Canada Post's sorting machinery. This could possibly delay or even prevent their mail being delivered.
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