Check Digits Definition

A check digit is a form of verification that is used to ensure the accuracy of data that has been inputted into a system. Check digits are often used in identification numbers, such as credit card numbers or social security numbers. By running a check digit algorithm, the system can verify that the number entered is correct.

There are many different ways to calculate check digits, but one common method is known as the Luhn algorithm. To generate a check digit using the Luhn algorithm, the digits in the number to be checked are added together, starting from the right-most digit. Every other digit is doubled during this process. If any of these doubled digits are greater than 9, they are subtracted from 9 (for example, 8 x 2 = 16; 16 – 9 = 7). Once all of the digits have been added together (including the check digit), the resulting sum should be divisible by 10.

The Luhn algorithm is just one example of how check digits can be calculated. There are many other methods that can be used, and different systems may use different algorithms. However, all check digit systems serve the same purpose: to verify that data has been inputted correctly into a system.