I’ve been familiar with the concept, but this is by far the best behind-the-scenes explanation I’ve seen.
I’m insulted they thought I didn’t know what a LUHN check is.
Of course, my current credit cards don’t even have a magnetic stripe, so the original purpose for the check digits is history. Still useful for ither situations where the number might get garbled though.
The other thing useful about credit cards is that the first set of digits refer to the issuer, not your account. Once you strip off the issuer code and the check digit, there’s much less that’s unique to your card.
Brad@beehaw.org 3 days ago
A car’s 17-digit VIN has a similar feature, for model years since 1981.
The 9th digit is the check digit, and it’s a much more complex algorithm (since the VIN can have numbers and letters.)