Check-Digit Tests › CheckDigit Calculation › Using the Modulo10 and Modulo11 Checkdigit Tests

Using the Modulo10 and Modulo11 Checkdigit Tests

The algorithm used for the CA Ideal modulo 10 and modulo 11 check‑digit test uses the following logic:

The number to check is assumed to contain the check‑digit in the low order (right‑most) position. The calculation begins with the second digit from the right and proceeds through the high order (left‑most) position. The loop used is:

SET SUM = 0
SET MULTIPLIER = 2
position on first digit
LOOP WHILE digits remain
   SET PRODUCT = MULTIPLIER * DIGIT
   SET SUM = SUM  PRODUCT
   IF MULTIPLIER LT 7
      SET MULTIPLIER = MULTIPLIER  1
   ELSE
      SET MULTIPLIER = 2
   ENDIF
   position on next digit
ENDLOOP
SET REMAINDER = $REMAINDER(SUM,DIV=11)
IF REMAINDER NOT = 0
   SET REMAINDER = 11 ‑ REMAINDER
ENDIF
SELECT FIRST ACTION
   WHEN REMAINDER EQ 10
      not eligible for Modulo‑11 check‑digit test
   WHEN CHECK‑DIGIT NOT = REMAINDER
      panel field has a check‑digit error
   WHEN OTHER
      check‑digit is correct
ENDSEL