HP 3000 Manuals HP 3000 Manuals
MODULUS 11
Modulus 11 detects single digit errors, single transpositions, and double
transpositions. Unlike other check digit systems, it is based on a
weighted checking factor for each digit in the basic number. The modulus
11 check digit is obtained as follows:
* Each digit position of the basic number is assigned a weighted
checking factor. The following factors are assigned, starting with
the units digit and progressing toward the high-order digit:
2 3 4 5 6 7 2 3 4 5 6 7 2 3 4...
* Each digit in the basic number is multiplied by its checking factor.
* The products are summed and then divided by 11. The remainder is
subtracted from 11. The result is the check digit.
Example
Assume a basic number 5 1 6 1 9 2 8 7 2
Checking factors 4 3 2 7 6 5 4 3 2
Add the products 20+3+12+7+54+10+32+21+4=163
Subtract remainder from 11 11-9=2
Check digit = 2
Self-checking number 5161928722
If a check digit is generated using modulus 11 calculations and the
result is 10, the check digit cannot be used and an error is returned.
Modulus 11 check digits are the remainder from dividing the product of
the calculations by 11 (see example above). Thus, if check digits are
being generated for a continuous series of numbers, every eleventh number
must be skipped to avoid this error.
If the product generated through the modulus 11 calculations is evenly
divisible by 11 (no remainder), the resulting check digit is 11. In this
case, the digit 0 is appended to the basic number.
To summarize, if the calculated check digit is 10, an error is returned;
if the calculated check digit is 11, a zero is appended to the basic
number.
When you attempt to add a modulus 11 check digit that evaluates to 10,
the reformatter issues the message: "Check digit is invalid for modulus
11 calculation".
If ENTRY checks a field according to the FORMSPEC statement CDIGIT 11 and
that field contains a value with a check digit that evaluates to 10, the
same message is issued.