---
name: "Algorithm::CheckDigits::M11_001"
section: "3pm"
platform: "linux"
package: "libalgorithm-checkdigits-perl"
version: "1.3.6-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Algorithm::CheckDigits::M11_001"
---

# Algorithm::CheckDigits::M11\_001(3pm)

compute check digits for ISBN, ISSN, VAT RN (PT), HKID (HK), Wagon number (BR), NHS (GB), VAT (SL)

## NAME

CheckDigits::M11\_001 - compute check digits for ISBN, ISSN, VAT RN (PT), HKID (HK), Wagon number (BR), NHS (GB), VAT (SL)

## SYNOPSIS

```
  use Algorithm::CheckDigits;
  $isbn = CheckDigits('isbn');
  if ($isbn->is_valid('3-88229-192-3')) {
        # do something
  }
  $cn = $isbn->complete('3-88229-192-');
  # $cn = '3-88229-192-3'
  $cd = $isbn->checkdigit('3-88229-192-3');
  # $cd = '3'
  $bn = $isbn->basenumber('3-88229-192-3');
  # $bn = '3-88229-192-'
```

## DESCRIPTION

### ALGORITHM

- 1\.

  The sequence of digits is processed right to left. Every digit is multiplied with their position in the sequence (i.e. the digit left to the check digit has the weight 2 then 3 etc.).

  With a Hongkong ID (hkid) the leftmost char is replaced with its position in the alphabet and then multiplied with 8 (its weight).

- 2\.

  The sum of all products is computed.

- 3\.

  The sum of step 2 is taken modulo 11.

- 4\.

  The checkdigit is the difference of the sum from step 3 to eleven under the following conditions:

  - isbn,issn

    If the difference is 10, the check digit is 'X'.

    If the difference is 11, the check digit is 0.

  - ustid\_pt

    If the difference is greater then 9, the check digit is '0'.

  - hkid

    If the difference is 10, the check digit is 'A'.

    If the difference is 11, the check digit is 0.

  - wagonnr\_br

    If the difference is 10, the check digit is 0.

    If the difference is 11, the check digit is 1.

  - nhs\_gb

    If the difference is 10, the number would not be taken.

    If the difference is 11, the check digit is 0.

  - vat\_sl

    This is a little bit unclear, don't trust on the method for this type.

### METHODS

- is\_valid($number)

  Returns true only if `$number` consists solely of numbers and the last digit is a valid check digit according to the algorithm given above.

  Returns false otherwise,

- complete($number)

  The check digit for `$number` is computed and concatenated to the end of `$number`.

  Returns the complete number with check digit or '' if `$number` does not consist solely of digits and spaces.

- basenumber($number)

  Returns the basenumber of `$number` if `$number` has a valid check digit.

  Return '' otherwise.

- checkdigit($number)

  Returns the checkdigit of `$number` if `$number` has a valid check digit.

  Return '' otherwise.

### EXPORT

None by default.

## AUTHOR

Mathias Weidner, `"<mamawe@cpan.org>"`

## SEE ALSO

perl, CheckDigits, *www.pruefziffernberechnung.de*.