UPC codes unique identify an item or service amongst all those authorized and marked with a UPC value. The UPC value on an item or service is widespread across all stores that carry that products. What this means is that regardless which store you go to which has a certain type of products, the UPC value for that exact products will be the same.
SKU is for Stock-Keeping Model and it is a value that is created for each products in a shop's products on hand by the keep itself. What this implies is that SKU's are keep particular, and not widespread like UPC's.

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barcodes