This website provides a facility for computing the eighth digit of an ISSN number, given the first seven numbers.

ISSN stands for 'International Standard Serial Number', and is a number that is assigned to a serial publication such as an
online journal. The format for an ISSN is given by:

xxxx-xxxy

, where x is a number in the range 0-9, and y is either a number
in the range 0-9 or the letter X. The value of the digit y is called the check digit. The sole function of the ISSN Calculator
available in this site is to compute this value. On applying for an ISSN number, an applicant is issued with a unique sequence of
seven numbers. It is then left to the applicant to compute the check digit. The ISSN web site whose English home page is located
here, serves at least two purposes: (a) it provides a precise and clearly stated
algorithm for computing the check digit given the first seven numbers, and (b) it provides a facility for checking if a given ISSN is
in fact a valid ISSN number. The ISSN Calculator, on the other hand, embodies the automation of the steps that are involved in going
through the algorithm, and thereby, spares the user the inconvenience and frustration caused by errors, which might arise in carrying
out the calculation by hand.