Data entry check digits, also known as verification digits or data entry verification codes, are special digits included in data to help prevent and detect errors during manual data entry. They are commonly used in applications where accurate data input is essential to avoid mistakes and maintain data integrity. Data entry check digits are calculated based on the other data digits and serve as a safeguard against input errors.
Why is a check digit important?
Luhn’s Algorithm
Luhn’s algorithm is a credit digit algorithm that uses modulo to detect simple errors. It is commonly used on 15 digit credit card numbers to automatically calculate the 16th digit.
Algorithm Steps
Write all the digits down in order.
For each number in the sequence that is in an odd position (first, third, fifth,etc) multiply that number by two and add each of the digits of the result together.
For each number in the sequence that is in even position, leave it as is.
Now add up all the resultant numbers together (including the ones you left as is)
Work out 10 minus modulo 10 of the total ( = 10 – Total MOD 10 )
The answer becomes the16th digit.
Luhn algorithm
The calculation of a involves performing mathematical operations on the other digits in the number.
Check Digit Use Cases
Credit Card Validation
Data entry check digits are commonly used in credit card numbers to ensure the validity and accuracy of the card data during transactions. The Luhn algorithm, for example, verifies that credit card numbers are correctly entered, reducing the risk of payment errors.
ISBN Validation
The International Standard Book Number (ISBN) includes a check digit to verify the accuracy of book identification numbers. This helps ensure that books are correctly identified in libraries and databases.
Barcodes and UPCs
Product barcodes, particularly the Universal Product Code (UPC), often include check digits to prevent errors during product scanning and inventory management. The check digit ensures that the barcode data is correctly entered or scanned, reducing errors in retail and logistics.
(ISBN & Barcodes use a x3 multiplier instead of x2)
What is the purpose of a check digit in a barcode?
