Editing PostBar (section)

==Character sets==
[[Image:CPC PostBar character chart.png|right|300px|thumb|Chart of PostBar characters]]
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 [[Canadian postal code|postal code]]s and [[country code]]s.  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 IDs for Canada Post's internal uses.

The bars making up a character can be interpreted as base-3 digits.  A full height bar encodes 0, a short lower bar (an ascender) encodes 1, and a short upper bar (a descender) encodes 2.  The leftmost bar in a group is the most significant [[ternary numeral system|trit]], and may have the value 3, with both upper and lower bars short (a tracker).

In other words, short upper and lower bars are assigned weights of 18 & 9, 6 & 3, and 2 & 1, from left to right.  Since the first bar has 4 possible values, and the following bars have 3, 2 bars can encode 4×3&nbsp;= 12 values, while 3 bars can encode 4×3×3&nbsp;= 36.

N characters are simply encoded as the values 0–9.  Only the value 9 requires a leading 3.

Z characters use the full 36 combinations representable by 3 bars.  The values 0–25 encode the letters A–Z, and 26–35 encode the digits 0–9.

A characters have a somewhat peculiar encoding.  They can also be decoded as three base-3 digits (a leading 3 is never used), with the values 2–26 mostly encoding A–Y.  Exceptions are that 0 encodes M, 1 encodes H, 9 encodes Z (rather than H), and code 14 is not used (rather than encoding M).
<!-- Presumably this has something to do with the two urban postal codes of Toronto (M) and Monteral (H). -->