![]() ![]() The substitution digits, that is, the results of the double and reduce procedure, were not produced mechanically. The device took the mod 10 sum by mechanical means. ![]() The algorithm appeared in a United States Patent for a simple, hand-held, mechanical device for computing the checksum. Therefore, systems that pad to a specific number of digits (by converting 1234 to 0001234 for instance) can perform Luhn validation before or after the padding and achieve the same result. The Luhn mod N algorithm is an extension that supports non-numerical strings.īecause the algorithm operates on the digits in a right-to-left manner and zero digits affect the result only if they cause shift in position, zero-padding the beginning of a string of numbers does not affect the calculation. Other, more complex check-digit algorithms (such as the Verhoeff algorithm and the Damm algorithm) can detect more transcription errors. It will detect most of the possible twin errors (it will not detect 22 ↔ 55, 33 ↔ 66 or 44 ↔ 77). It will not, however, detect transposition of the two-digit sequence 09 to 90 (or vice versa). The Luhn algorithm will detect most single-digit error (except for 0↔5 with a multiplier of 2), as well as almost all transpositions of adjacent digits. ![]()
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