Pitney Bowes J640 - Manual (Page 78)

4. Divide the sum of the products by the modulus (10 in this
case), only to the whole number. The balance is called
the remainder.
9
10 98
90
8
5. Subtract the remainder from the modulus.
The result becomes the check digit. In this case, the
check digit is 2.
10 - 8 = 2
J640 Programmer’s Manual
3-4