You should also take into account that even that only applies to UPC-A barcodes.  Not everything you see with a bar code follows that standard.  Working in a small business that designs, builds, assigns part numbers, and sells items; I put whatever part number and barcode on our product that makes sense to *us*.  Our barcodes don't follow any of those standards, and you'll find the same situation with many other products.  That being said, you can tell the difference because we don't label our barcodes "UPC".  Just something to think about.