# CheckDigit

The CheckDigit package provides a set of functions to calculate check
digits according to various algorithms and to verify whether a value
ends in a valid check digit.

The following algorithms have been implemented:

**Verhoeff** The Verhoeff algorithm is appropriate for
numerical data and detects all single-digit substitutions (x to y) and
adjacent digit transpositions (xy to yx). In addition, the Verhoeff
check digit can detect most twin errors (xx to yy), jump twin errors
(xyx to zyz), jump transpositions (xyz to zyx), and phonetic errors
(‘sixty’ to ‘sixteen’).

## References

Verhoeff, J. “Error Detecting Decimal Codes”, Mathematical Centre
Tract 29, The Mathematical Centre, Amsterdam, 1969.