The Calculate Modulus 11 command calculates the value for a Modulus 11
Self-Check Digit. The command returns a value for the self-check digit which is
intended to be added to a number such as a customer number. DDS supports the
CHECK(M11) keyword for a field to assist in ensuring the number is keyed
correctly. Some input values cannot produce a Modulus 11 self-check digit and
an escape message will be sent.