HP Data Entry and Forms Management System (VPLUS) Reference Manual (32209-90024)

Appendix D 581
CHECK DIGIT CALCULATION
MODULUS 11
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:
234567234567234...
• 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
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.
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