Being a software Engineer or a computer science students everyone would have came across the term Error Detection Code or Technique which is widely used.
Recently I just came to know the technique used in ISBN number system to handle errors.
ISBN is International Standard Book Number which is used to identify each book uniquely. We had 10 digit ISBN format number developed by ISO, now we currently using 13 digit ISBN number format which is compatible with EAN-13
Now let us just look only on how the error detection is done in ISBN 10 digit format.Consider the below image
2-1234-5680-2 is the ISBN 10 digit format, here the last digit 2 is the check digit, the numbers before that represents various parameters like Group, Publisher, Title.
The magic number used here for Error Detection is 11. Yes it is 11.
Lets see how it is done,
( N1*10 + N2 * 9 +........ + N9*2 + N10 * 1 ) mod 11 = 0, N10 is the check digit which would be chose accordingly so that the end of the expression inside the bracket always results as a multiple of 11.
N10 is anynumber between 0 -10, but incase of 10 we use X - Roman equivalent to denote 10 so that ISBN remains 10 digit.
= 2 * 10 + 1 * 9 + 2 * 8 + 3 * 7 + 4 * 6 + 5 * 5 + 6 * 4 + 8 * 3 + 0 * 2 + 2 * 1
= 20 + 9 + 16 + 21 + 24 + 25 + 24 + 24 + 0 + 2
= 165
= 165 mod 11 = 0
Recently I just came to know the technique used in ISBN number system to handle errors.
ISBN is International Standard Book Number which is used to identify each book uniquely. We had 10 digit ISBN format number developed by ISO, now we currently using 13 digit ISBN number format which is compatible with EAN-13
Now let us just look only on how the error detection is done in ISBN 10 digit format.Consider the below image
2-1234-5680-2 is the ISBN 10 digit format, here the last digit 2 is the check digit, the numbers before that represents various parameters like Group, Publisher, Title.
The magic number used here for Error Detection is 11. Yes it is 11.
Lets see how it is done,
( N1*10 + N2 * 9 +........ + N9*2 + N10 * 1 ) mod 11 = 0, N10 is the check digit which would be chose accordingly so that the end of the expression inside the bracket always results as a multiple of 11.
N10 is anynumber between 0 -10, but incase of 10 we use X - Roman equivalent to denote 10 so that ISBN remains 10 digit.
= 2 * 10 + 1 * 9 + 2 * 8 + 3 * 7 + 4 * 6 + 5 * 5 + 6 * 4 + 8 * 3 + 0 * 2 + 2 * 1
= 20 + 9 + 16 + 21 + 24 + 25 + 24 + 24 + 0 + 2
= 165
= 165 mod 11 = 0