POSTNET
Height modulation rather than bar width carries the data in POSTNET, the United States Postal Service symbology in which every bar has the same thickness and meaning is conveyed by whether a bar is tall or short. Five bars encode each digit, and a symbol holds five, nine, or eleven digits corresponding to a ZIP code, ZIP+4, or full delivery point. The Postal Service introduced the format in 1983 and retired it in 2013 in favour of Intelligent Mail. Bars stand 3.175 mm tall at a 0.38 mm X-dimension, and quiet zones are specified in millimetres rather than modules because the symbol is printed on envelopes rather than packaging. POSTNET encodes digits only and is not a GS1 data carrier.
A height-modulated barcode used by the United States Postal Service to encode ZIP codes for automated mail sorting. POSTNET uses tall and short bars rather than varying widths, and was the primary US mail sorting barcode from 1983 until its replacement by Intelligent Mail in 2013.