Plessey Code — format provenance and usability ========================================================================== This file records where the Plessey Code symbology comes from, what governs it, and the basis on which this project implements and redistributes it. It is an ENGINEERING INVENTORY, NOT LEGAL ADVICE. Items marked [TO VERIFY] have not been independently confirmed by the author. ORIGIN -------------------------------------------------------------------------- Developed in 1971 by the Plessey Company of England. Its Modified Plessey descendant, developed by the MSI Data Corporation, is already implemented in this SDK as `msi` (`licenses/msi-plessey.license`) — this is the originating format that MSI is a variant of, from the same era and company lineage this project already treats as freely implementable. [TO VERIFY] SPECIFICATION -------------------------------------------------------------------------- No ISO/IEC standard exists for Plessey, the same as its MSI descendant. It is documented through vendor and industry publications rather than a formal standard. [TO VERIFY] Specification TEXT is copyrighted by its publisher. The SYMBOLOGY it describes is not — an encoding scheme is a system, not a work of authorship. This project implements the symbology; it does not reproduce, redistribute or excerpt any specification document. PATENT STATUS -------------------------------------------------------------------------- The originating patents date from 1971 and are understood to have expired, the same basis already relied on for MSI. [TO VERIFY] TRADEMARK -------------------------------------------------------------------------- No live trademark restriction on implementing Plessey is known to the author. [TO VERIFY] That is a statement about the author's knowledge, not a finding that no mark subsists: no trademark search was carried out. The Plessey Company was absorbed into other businesses in the 1980s-90s and is understood no longer to exist as an independent entity. [TO VERIFY] A trademark does not restrict implementing a symbology. It restricts branding — how a product names and presents itself. IMPLEMENTATION BASIS IN THIS PROJECT -------------------------------------------------------------------------- Plessey Code is implemented here from published descriptions of the format, which are systems and facts rather than works of authorship. The sixteen-value reversed-BCD digit table and guard frame are original Sythos data, cross-checked against Zint (libzint, BSD-3-Clause) as an independent black-box reference and against a second, independent technical description before being written — not copied. The mandatory CRC-8 check (generator polynomial x^8+x^7+x^6+x^5+x^3+1) is computed with an original Sythos bitwise implementation of the standard polynomial-division algorithm; the polynomial itself is a published, public technical fact, cross-verified across two independent sources plus Zint's own generator constant. No source code or constant table from any other barcode implementation is copied or shipped. CONCLUSION -------------------------------------------------------------------------- On the basis of the references below, and consistent with the trust bar already applied to its MSI descendant in this SDK, Plessey Code is understood to be freely implementable and redistributable. This project's implementation of it is distributed under the MIT License with no additional restriction. References relied upon: - Published descriptions of the Plessey symbology [TO VERIFY] - The CRC-8 generator polynomial, cross-verified across two independent public technical descriptions This is an engineering assessment, not legal advice. Items marked [TO VERIFY] have not been independently confirmed by the author. If your use is commercially sensitive, obtain your own legal review.