What is a check digit?

A check digit is a digit added to a number sequence to enhance the error detection process. In the following, we will explain what the check digit is, its purpose, and examples of its implementation.

What does check digit mean?

A check digit is a form of redundancy check that helps to ensure that a given number sequence is error-free and complete. It is typically a single digit added to the end of a number sequence, computed from the other digits in the sequence using a check digit algorithm. The check digit is used by computers to validate the accuracy of the input data and detect any errors that may have occurred during data entry, transmission, or storage.

Check digit examples

One example of check digit implementation is the International Standard Book Number (ISBN) used in the book publishing industry. The ISBN-13 consists of 13 digits, including a check digit, which is calculated based on the preceding 12 digits using the Modulo 10 algorithm. The Modulo 10 algorithm uses a combination of weighted sums and division remainders to generate the check digit. Another example of the check digit method is the Universal Product Code (UPC) used in retail, which contains a 12-digit number and a check digit. Learn more about the UPC here.

Check digit history

The concept of check digit dates back to the early days of computing, when data entry was done manually and errors were common. The first implementation of check digit was by American Airlines in the early 1960s, to help reduce errors in their ticketing system. Today, check digits are widely used in various industries, including retail, healthcare, transportation, and logistics, to ensure the accuracy and completeness of data.