In a serials union list project that I was working on last year I built
a database of serial bibliographic records and a second dB of holdings
records linked to the biblio records by ISSN.  To speed up the report
I sorted the biblio file (not the Library Corp. product!) by ISSN and
discovered that I had many runs of several consecutive ISSNs up to the
7th digit and that the 8th appeared to be a check digit.  The same
relationship which may be seen in ISBN and barcode check digits could
be seen in the 8th digit.  Someone correct me if I am wrong, but it
sure LOOKS like the 8th digit is a check!

Charley Pennell          cpennell@kean.ucs.mun.ca
Memorial University of Newfoundland