MaxiCode Source: en.wikipedia.org/wiki/MaxiCode

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MaxiCode is a public domain, machine-readable symbol system developed by United Parcel Service (UPS) in 1992.^[1] Designed for tracking and managing package shipments, it resembles an Aztec Code or QR code but uses dots in a hexagonal grid instead of square grid. It is standardized under ISO/IEC 16023.^[2][3]

A MaxiCode symbol—also called "Bird's Eye", "Target", "dense code", or "UPS code"—is a 1-inch square with a central bullseye surrounded by hexagonal dots. It stores about 93 characters, and up to 8 symbols can be linked to carry more data. The symmetrical bullseye aids in fast, accurate scanning, even on moving packages.

MaxiCode symbols using modes 2 and 3 include a Structured Carrier Message containing key information about a package. This information is protected with a strong Reed–Solomon error correction code, allowing it to be read even if a portion of the symbol is damaged. These fields include:

1. A 4-bit indication of the mode in use, currently either mode 2 or mode 3.
2. A national or international postal code. MaxiCode supports both numeric postal codes (e.g. a ZIP Code), and alphanumeric postal codes.
3. A 3-digit country code encoded per ISO 3166
4. A 3-digit class of service code assigned by the carrier

The structured portion of the message is stored in the inner area of the symbol, near the bull's-eye pattern. (In modes that do not include a structured portion, the inner area simply stores the beginning of the message.)

Irrespective of mode, a variable amount of application-specific information can be encoded in a MaxiCode symbol. This format of this additional data is not strictly defined, and amongst other information may include:

• Purchase order number
• Customer reference
• Invoice number
• Tracking number
• Indicator of the originating carrier

• Mode 0 – Obsolete; replaced by Modes 2 and 3. Older printers with outdated firmware may still produce it. Identifiable by two white horizontal hexagons in the upper right corner (black in all other modes).^[4]
• Mode 1 – Obsolete; replaced by Mode 4.
• Mode 2 – Structured Carrier Message with numeric postal code (mainly for U.S. domestic use).
• Mode 3 – Structured Carrier Message with alphanumeric postal code (mainly for international use).
• Mode 4 – Unformatted data with Standard Error Correction.
• Mode 5 – Unformatted data with Enhanced Error Correction.
• Mode 6 – Used for programming hardware devices.

UPS labels use Mode 2 or 3 MaxiCodes.

• Source for official MaxiCode technical specification
• Information about MaxiCode is available in US Patents U.S. patent 4,874,936, U.S. patent 4,896,029, and U.S. patent 4,998,010