MOD 11 Check Digit Method

DURING INPUT TWO KINDS OF ERROR ARE VERY COMMON

i. TRANSACTION ERROR    ii. TRANSPOSITION ERROR DETECTED USIN CHECK DIGIT,

--A CHECK DIGIT IS AN ADDITIONAL CHARACTER(MOSTLY A DIGIT) IS INTRODUCED INTO THE INPUT DATA.

*BOTH THESE ERRORS CAN BE DECTECTED

Example: find the check digit for the number 036532

0	3	6	5	3	2
x7	x6	x5	x4	x3	x2
0	18	30	20	9	4

0 + 18 + 30 + 20 + 9 + 4 = 81
81/11 = 7 remainder 4
11 - 4 = 7

7 is therefore the check digit.

PROBLEMS: If the remainder from the division is 0 or 1, then the subtraction will yield a two digit number of either 10 or 11. This won't work, so if the check digit is 10, then X is frequently used as the check digit and if the check digit is 11 then 0 is used as the check digit. If X is used, then the field for the check digit has to be defined as character (PIC X) or there will be a numeric problem.

Steps to verify if the check digit is included as part of the number:

• The entire number is multiplied by the same weights that were used to calculate and the check digit itself is multiplied by 1.
• The results of the multiplication are added together.
• The sum is divided by 11 and if the remainder is 0, the number is correct.

PROBLEM: Note that if the check digit is X then 10 is used in the multiplication. Code for this occurrence must be included.

Example of verifying the number 0365327 where 7 is the calculated MOD11 check digit:

0	3	6	5	3	2	7
x7	x6	x5	x4	x3	x2	x1
0	18	30	20	9	4	7

0 + 18 + 30 + 20 + 9 + 4 + 7 = 88
88/11 is 8 remainder 0

Since the remainder from this calculation is 0, the check digit 7 is valid.