KeyesPunch(tm) - FAQ

Self Check Digit

Which Modulus 10 self-check digit formula is used in the program

To compute the standard modulus 10 self-check digit, do the following:

1. Multiply the units position and every alternate position of the base number by 2.
2. Add the digits in the products to the digits in the base number that were not multiplied.
3. Subtract the sum from the next higher number ending in 0.

The difference is the self-check digit.

For example:

Base number                6 1 2 4 8

Units position and         6   2   8
every alternate position

Multiply by 2              12  4   16

Digits not multiplied        1   4

Add                        1 + 2 + 1 + 4 + 4 + 1 + 6 = 19

Next higher number         20
ending in 0

Subtract                   19

Self-check digit           1

Which Modulus 11 self-check digit formula is used in the program

To compute the standard modulus 11 self-check digit, do the following:

1. Assign a weighting factor to each digit position of the base number. These factors are: 2, 3, 4, 5, 6, 7, 2, 3, 4, 5, 6, 7, 2, 3, ... starting with the units position of the number and progressing toward the high-order digit. For example, the base number 991246351 would be assigned the weighting factors as follows:

   Base number           9 9 1 2 4 6 3 5 1
   
   Weighting factor      4 3 2 7 6 5 4 3 2

2. Multiply each digit by its weighting factor.
3. Add the products.
4. Devide this sum by 11.
5. Subtract the remainder from 11.

The difference is the self-check digit.

For example:

Base number                1 3 7 3 9
Weighting factors          6 5 4 3 2

Multiply                   6 15 28 9 18
Add                        6 + 15 + 28 + 9 + 18 = 76

Devide                     76/11 = 6 plus a remainder of 10

Subtract                   11 - 10 = 1

Self-check digit           1

Note: If the remainder from step 4 is 0, the self-check digit is 0. If the remainder is 1, the base number has no self-check digit; you must ensure that the base numbers with remainders of 1 in step 4 are not used in the fields you define as self-check fields.