What is the barcode that appears most frequently on magazine covers?
Based on an informal sample I took, it does not seem to be either SICI
or EAN-13.  Instead I see a lot of 13 digit codes that don't conform to
the structure of EAN-13.  I also see a lot of 15 digit codes.  Are these
UPC codes?  Do UPC codes contain ISSN information?  How are these bar
codes used for check-in purposes?

Thank you

Graham Barr <graham@DRA.COM>