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# NAME

CheckDigits::M11_008 - compute check digits for VAT Registration Number (DK)

# SYNOPSIS

``````  use Algorithm::CheckDigits;

\$ustid = CheckDigits('ustid_dk');

if (\$ustid->is_valid('13585628')) {
# do something
}

\$cn = \$ustid->complete('1358562');
# \$cn = '13585628'

\$cd = \$ustid->checkdigit('13585628');
# \$cd = '8'

\$bn = \$ustid->basenumber('13585628');
# \$bn = '1358562';
``````

# DESCRIPTION

## ALGORITHM

1. Beginning left every digit is weighted with 2, 7, 6, 5, 4, 3, 2, 1

2. The weighted digits are added.

3. The sum from step 2 is taken modulo 11.

4. The number is valid if the sum from step 3 is zero (0).

## METHODS

is_valid(\$number)

Returns true only if `\$number` consists solely of numbers and the sum computed according to the algorithm given above is 0.

Returns false otherwise,

complete(\$number)

Returns `\$number` if `\$number` is valid according to the algorithm given above.

Return '' otherwise.

basenumber(\$number)

Returns `\$number` if `\$number` is valid according to the algorithm given above.

Return '' otherwise.

checkdigit(\$number)

Returns '' if `\$number` is valid.

Return undef otherwise.

None by default.

# AUTHOR

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