أول 25 من الأرقام التسلسلية

Serial numbers only become necessary once parts are interchangeable. While a musket was fitted by hand, every lock was unique and nobody needed to say which one; the moment any lock fits any musket, a label is the only way left to speak about a particular object.

The French gunsmith Honoré Blanc built interchangeable musket locks in the 1780s and demonstrated them in Paris in 1785 to Thomas Jefferson, then the American minister to France, who wrote home about it with some enthusiasm. The American version of the story is usually told about Eli Whitney, who took a government musket contract in 1798 and staged a demonstration of interchangeable parts for officials in 1801. Historians of technology — Robert Woodbury in 1960 and Merritt Roe Smith in the 1970s among them — have argued that the demonstration was misleading and that Whitney's parts were in fact hand-fitted. Genuinely machine-made interchangeability arrived later, through Simeon North and through John H. Hall's work at the Harpers Ferry armory in the 1820s and 1830s.

Law caught up unevenly. In the United States the National Firearms Act of 1934 required serial numbers on the weapons it covered, and the Gun Control Act of 1968 extended the requirement to every firearm made or imported by a licensee. Vehicles were standardised later still: the seventeen-character VIN, settled by ISO 3779 and by American regulation for the 1981 model year onward, omits the letters I, O and Q so that they cannot be misread as digits, and in North America reserves its ninth character for a check digit.

The check digit itself has a named author. Hans Peter Luhn, an engineer at IBM who also did foundational work on automatic indexing, filed in 1954 for the "computer for verifying numbers" granted as US Patent 2,950,048 in 1960. His rule — double every second digit from the check position leftward, subtract nine wherever doubling passes nine, and choose a final digit that brings the total to a multiple of ten — now guards credit card numbers and the fifteen-digit IMEI of every mobile handset.

الخصائص الرئيسية

• The Luhn check digit is chosen so that, doubling every second digit from the check position leftward and subtracting 9 from any doubled result above 9, the whole sum is a multiple of 10.
• Luhn catches every single-digit error and every transposition of two adjacent digits except 09 for 90; it also misses the twin errors 22 for 55, 33 for 66 and 44 for 77, so it detects mistakes rather than guaranteeing correctness.
• A modern VIN is 17 characters and never contains I, O or Q, precisely because they can be read as 1 and 0; in North America its ninth character is a mandatory check digit, which ISO 3779 itself does not require.
• An IMEI is fifteen digits: an eight-digit type allocation code, a six-digit unit serial and a Luhn check digit.
• Hans Peter Luhn’s check-digit patent, US 2,950,048, was filed in 1954 and granted in 1960; the algorithm has long since passed into the public domain.
• A serial number names one physical object and a part number names a design, so two units of the same part share a part number and never a serial.
• The pattern fields are {SEQ:n} for the padded counter, {YYYY}, {YY}, {MM} and {WW} for the build date code, {N:n} for digits, {A:n} for letters, {X:n} for letters and digits, {H:n} for uppercase hex and {LUHN} for a check digit over everything numeric to its left.
• With look-alike characters switched off, {X} draws from 34679ACDEFGHJKLMNPQRTUVWXY — 26 characters with the confusable 0/O, 1/I, 2/Z, 5/S and 8/B pairs removed.