Validation Algorithm

The algorithm for validating the two check digits of a reference number is as follows:

First Check Digit:

The first of the two check digits is calculated as:

MOD 10 [10 - MOD 10 (Y)]

where Y is the sum of the products obtained by multiplying the 3rd to the 10th digits of the reference number by the following weights:

Digit	Weight
3	9
4	7
5	8
6	6
7	7
8	9
9	6
10	8

Second Check Digit:

The second check digit is calculated as:

MOD 10 [10 - MOD 10 (Z)]

where Z is the sum of the following:

f(digit 1) + digit 2 + f(digit 3) + digit 4 +f(digit 5) + digit 6 + f(digit 7) + digit 8 +
f(digit 9) + digit 10 + f(first check digit)

The value of f(digit n) is determined as follows:

Digit	f(digit n)
0	0
1	2
2	4
3	6
4	8
5	1
6	3
7	5
8	7
9	9

The MOD 10 (n) operation yields a value that is the remainder after dividing n by 10. This remainder is the same as the low-order digit on n.

Example:

The following example illustrates the validation of the reference number 936125183702, where 0 is the first check digit and 2 is the second check digit.