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

Appendix D 579
CHECK DIGIT CALCULATION
D CHECK DIGIT CALCULATION
Check digits are digits added to the end of a value that contains only numbers (0-9) or
letters of the alphabet (A-Z). A FORMSPEC option can be selected that causes a modulus
check to be made on a value entered at the terminal.
Whenever a value is entered for which check-digit verification has been specified, a
modulus calculation is performed. The result of a modulus calculation is a single digit that
must match the last digit (the "check digit") of the entered value. If the match is not
successful, an error is diagnosed. Note that for modulus checks to be meaningful, the last
digit verified by such a check must have been calculated by the same method used for the
check.
REFSPEC has an option that lets you add a check digit to an entered value. The check
digit is added when REFORMAT is run. Thus, the check digit is added after the value is
entered at the terminal but before it is input to the application program. In this case, the
modulus calculation is made programmatically.
The modulus calculations used by VPLUS/V are either modulus 10 or modulus 11. A value
is checked by one or the other of these calculations, depending on which was used to add
the check digit. Thus, a value whose check digit was added using modulus 10 can be
checked only by modulus 10; and a value with a modulus 11 check digit can be checked
only with modulus 11 calculations.