Kontrollnummer

Kontrollnummer, often translated as control number or check number, is a numeric or alphanumeric identifier that includes a check digit (kontrollsiffra) produced by a calculation from the other digits. Its primary purpose is to detect errors in data entry, transcription, or transmission and to help validate that a number is correctly formed.

The check digit is generated by a specific algorithm and appended to the identifier. When the full number is later entered or scanned, the same algorithm can be re-applied to verify that the check digit matches the rest of the digits. This enables detection of common mistakes such as single-digit errors or transpositions of adjacent digits. Different systems use different algorithms, with some of the most common being the Luhn (modulus 10), Modulo 11, and Modulo 97 schemes.

Kontrollnummer are used in a wide range of contexts, including invoice reference numbers, bank account or payment identifiers, product codes, and barcodes. For example, barcodes such as EAN use a check digit calculated by a modulus 10 algorithm, while payment systems may use IBAN-style check digits computed through a modulus-based process. Invoices and other financial documents often rely on a kontrollnummer to ensure that references can be reliably reconciled.

Limitations include that a kontrollnummer improves error-detection but is not a security feature. It cannot prevent fraud, and some errors may still go undetected. Proper validation in software, along with other controls, is still required for robust data handling. See also check digit, reference number, and common algorithms like Luhn and Modulo 11.