Tarkistusnumeroiden

Tarkistusnumeroiden, known in English as check digits or check numbers, are a simple form of error detection used in identification numbers such as barcodes, credit card numbers, and ISBNs. They are a single digit or a few digits appended to a string of digits. Their purpose is to help detect accidental errors during manual data entry or transmission.

The check digit is calculated from the other digits in the number using a specific algorithm. When the number is entered or transmitted, the same algorithm is applied to the digits, and the result is compared to the appended check digit. If they do not match, it indicates that an error has occurred. This method is effective at catching common errors like single digit errors, transpositions of adjacent digits, and other simple mistakes.

Various algorithms are used to calculate check digits, with the most common being the Luhn algorithm, used for credit card numbers, and variations of weighted sums, used for ISBNs and UPC barcodes. The simplicity of these algorithms makes them easy to implement in both software and hardware, contributing to their widespread adoption. While check digits are not foolproof and cannot detect all possible errors, they significantly improve data integrity by catching a large percentage of common mistakes at a low cost. They are a fundamental component in ensuring the accuracy of many identification systems we rely on daily.