CHECK DIGIT INFORMATION

ABOUT CHECK DIGITS AND WHY THEY'RE IMPORTANT

What is a check digit?
A check digit is the result a mathematical calculation that is applied to a series of numbers. The most common check digit routine used in remittance processing is the Modulo 10, or Mod 10. When the bill that is sent to the customer is printed, this routine is performed on the scanline, and a check digit is calculated.

Why use a check digit?
There are two very important reasons for using a check digit:
     1. The integrity of the OCR scanline is ensured by using a
         Check Digit Verification routine.
     2. The chance of a misread scanline passing document
         validation is prevented because of CDV failure.

How does CDV work?
Let's say you have the following scanline:

By applying the following Mod 10 (1, 2, 1, 2...) routine to the scanline, we can calculate a check digit by multiplying the first number by 1, the second by 2, etc., and then add up the product:

Notice that there are two possibilities in the above example -- by using the remainder we have a check digit of 9, or by subtracting the remainder from the next highest factor of 10 we have a check digit of 1. Either one works.

Now let's use the remainder (9) and add it to the scanline:

In order for the document to pass validation, all numbers in the scanline must be read correctly by the OCR reader or CDV will fail and the document will stop. By using a check digit and a CDV routine we can be sure that all numbers in the scanline will be read correctly and that errors will not occur.

Another example using product digit add:

In this example we take an extra step by adding the digits of the product if there are two. For example, if you multiply 9 x 2 you add the 1 and 8 together to come up with 9. Then you add all those numbers together to calculate a check digit:

Omega Systems strongly recommends that you utilize one of the above methods to calculate a check digit in your scanline. Errors from misreads can be prevented, and better results from the remittance process will be achieved.

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Updated 06/06/2000