PostBar is one of the bar code systems used by Canada Post for mail sorting, along with CPC Binary. While CPC Binary is printed in a special ultraviolet-fluorescent ink, PostBar is a more "normal" black-ink-printed bar code. Like the Intelligent Mail barcode used by the USPS, PostBar uses bars which vary in length and in positioning (with ascenders and descenders from the base position), but has its own coding system for the meanings of the bars. Reed-Solomon error correction is used. Similar systems are used in other countries' postal systems, including Australia Post.
This sort of bar code system is regarded as "four-state" because there are four types of bars, classified by presence of ascenders and/or descenders. This sort of system is transcribable using DAFT notation.