The parameters for the MOD10 function are as follows:
Dir 0 = start on right
Dir 1 = start on left
Weight 0 = start with 2
Weight 1 = start with 1
Direction = 0 (right to left) Weight = 0 (start with '2') 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 End here ← ← ← ← ← ← ← ← ← ← ← ← Go this direction ← ← ← ← ← ← ← ← ← ← ← ← Start here Direction = 0 (right to left) Weight = 1 (start with '1') 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 End here ← ← ← ← ← ← ← ← ← ← ← ← Go this direction ← ← ← ← ← ← ← ← ← ← ← ← Start here Direction = 1 (left to right) Weight = 0 (start with '2') 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 Start here → → → → → → → → → → → → Go this direction → → → → → → → → → → → → End here Direction = 1 (left to right) Weight = 1 (start with '1') 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 Start here → → → → → → → → → → → → Go this direction → → → → → → → → → → → → End here
Ucompose uses the Luhn algorithm to calculate the check digit.
http://en.wikipedia.org/wiki/Luhn_algorithm
The following example assumes a weight of 0 and a direction of 0.
(2,1,2,1,... starting from the right)
Account number 0 0 4 1 7 8 0 0 0 0 0 0 0 0 0 1 3 0 3 7 x
Weight 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 x
Multiply by weight 0 0 4 2 7 16 0 0 0 0 0 0 0 0 0 2 3 0 3 14 x
Sum of digits 0 0 4 2 7 7 0 0 0 0 0 0 0 0 0 2 3 0 3 5 = 33
MOD10 check digit = 7
The check digit (x) is obtained by computing the sum of digits then computing 9 times that value modulo 10.
In equation form:
(33 * 9) mod 10
In algorithm form:
Compute the sum of the digits (33).
Multiply by 9 (297).
The last digit, 7, is the check digit.
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