5. Check Digit

This is used when you want to be sure that a range of numbers has been entered correctly for example a barcode or an ISBN number:

ISBN 1 84146 201 2

The check digit is the final number in the sequence, so in this example it is the final ‘2’.

bar code check digit

The '6' on the right is the check digit.

The computer will perform a complex calculation on all of the numbers and then compare the answer to the check digit.  If both match, it means the data was entered correctly. 

Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: Check Digit