is checked by using the Verhoeff check
, which is a Dihedral D 5 Check. This detects a higher proportion of common typographical errors than either the IBM or Modulus 11 check. Unlike the Modulus 11 check it is effective on decimal strings longer than ten-digits. Furthermore its value can always be represented as a decimal digit without excluding any values.
See Check-Digit Computation for detailed information about the Verhoeff check-digit algorithm and links to sample program code.
- See http://snomed.org/verhoeff for a sample web form that can be used to compute a check-digit or check the validity of an .