How do UPC/EAN codes work?

When I had Nero 6.3.1.25, I was able to create custom UPC/EAN codes for use on my Audio CDs. I use them to better recognize when and what CD I have burnt. Unfortunately Nero 6.6.0.0 tells me my codes are not valid. What is the algorithm used to create a “valid” UPC/EAN code ?

http://www.adams1.com/pub/russadam/upccode.html

http://www.binsales.com/upc.htm - calculate check digit (UPC-12)
http://electronics.howstuffworks.com/upc1.htm

A few to be going on with - I wonder if by “not valid”, they mean it fails the checksum digit test, as I doubt they bother checking that it’s really a code for a CD ?

Probably best to use the instore codes (since these are locally assigned by definition)

Yes, it fails the checksum. This is because I create my UPC codes by putting in the burning date (22102004) + the number of my CD (00025)… and I was doing this ignoring the checksum test :stuck_out_tongue:

thanks :wink: