Simple sum solves bank card errors
Mistyping a single digit of your bank card number or swapping two adjacent digits will account for almost 90% of errors at the Christmas checkout – but a simple 1960’s algorithm catches them

WHAT DO CARD DIGITS MEAN?
Major Industry Identifier (one digit)
1, 2 Air travel, financial
services
2, 5 Mastercard
3 AMEX, Diners Club
4 Visa
6 Discover
7 Petrol
8 Healthcare, telecoms
9 Government
Issuer Identifier
Six
Financial institution, credit or debit card, country of origin
Account number
Check Digit
One
Used to validate entire number using Luhn algorithm

LUHN ALGORITHM
Validates card number by checking for accidental errors in sequence
Starting from Check Digit on right
Double the value of every other digit
Add values of each doubled digit, each undoubled digit and Check Digit
If resulting number ends in zero, card number is validated
With all other numbers being pre-determined, Check Digit ensures validation
Sources: Scientific American, Stripe, Vanquis
Picture: Getty Images
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