>>> I presume you'll use Code 39. However, which code you use depends on how much you want to store in the code. 39 is common, I believe, for inventory management in the U.S. <<
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>Correct. The Universal Product Code (UPC) bar codes you see on grocery items are code 39. It isn't truly universal -- the UK has its own standard for grocery products, as do other countries -- but in the U.S. it is pretty darn close to universal. Most if not all of the big grocery chains stopping carrying items without UPC codes 20 years ago.

Actually, that's not quite correct. UPC is one barcode symbology. Code39 is another. UPC-A (most commonly in US) is 12 digits, where EAN-13 (the European standard) is 13 characters. U.S. UPC-A codes are compatible with EAN-13 since the U.S. EAN equivelent is "0" + UPC-A.

UPCs (and EANs) are controlled. You can't use just any old number, though there are some in-store use sequences.

Code-39 is used to encode whatever you want, as long as it's a short string. Check out the references I posted in my other post.