Example: Calculation of the Check Digit

This example illustrates the calculation of a check digit.

Reference number (invoice number): 4 5 3 2 1 2 3 4

The system:

1. Assigns weights from right to left:

   Digit	Digit	Digit	Digit	Digit	Digit	Digit	Digit
   4	5	3	2	1	2	3	4
   3	7	1	3	7	1	3	7

2. Multiplies each digit of the reference number by the corresponding weight:

   Digit	Digit	Digit	Digit	Digit	Digit	Digit	Digit
   4	5	3	2	1	2	3	4
   3	7	1	3	7	1	3	7
   12	35	3	6	7	2	9	28

3. Adds the resulting numbers: 12 + 35 + 3 + 6 + 7 + 2 + 9 + 28 = 102.

4. Rounds up the sum to the nearest 10: 110.

5. Subtracts the sum from the rounded number: −102.

The difference is the check digit: 8.

The full reference number is 4 5 3 2 1 2 3 4 8.