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When I worked at a grocery store in the 2000s, you didn't need the checksum digit when keying in a barcode by hand. In fact, manually entering the checksum digi

When I worked at a grocery store in the 2000s, you didn't need the checksum digit when keying in a barcode by hand. In fact, manually entering the checksum digit would result in a "product not found" error. So I wonder if the checker had to manually look anything up, assuming it was only the checksum digit that was frayed off. Perhaps some POS systems do require the checksum digit for manually-entered barcodes, though.

akoboldfrying 3y ago
>In fact, manually entering the checksum digit would result in a "product not found" error. That is hilarious to me. The obviously safer approach of checking the check digit was not merely neglected, but actively forbidden.
- lifthrasiir 3y ago
  It is possible that a check digit could happen to be incorrect from the beginning. This (and more rarely, an accidental code reuse) does happen fairly commonly with ISBN, so I would expect the same for general UPC/EAN.
- efreak 3y ago
  Barcodes are entered as text. Older barcode scanners used to plug into either the serial port or the PS2 keyboard port; often they had an inline adapter so you could plug it in between your computer and keyboard. As a checksum, the last digit of the barcode is not part of the data (product number), it's metadata; when the barcode reader beeps, that means it has computed the check digit and it matches the digit on the barcode. The barcode data is sent to the computer, but the check digit is not. The check digit is not in the database. The computer using the UPC leaves it to the barcode reader or human to ensure the input is correct. You'll might also notice that similar barcodes exist in multiple places as well--unopened cases of products might have an identifier that includes the UPC, and so does the price sticker on the shelf. Both of these include more data than just the UPC.
andirk 3y ago
As a grocery checker, I also remember not typing the checksum. It isn't part of the product's ID, but manually typing in probably has a higher chance of error than scanning so what the heck?? Another fun fact: in the intro to The Simpsons, Maggie gets scanned by the clerk as a valid item with a price shown on the register.

akoboldfrying 3y ago

>In fact, manually entering the checksum digit would result in a "product not found" error. That is hilarious to me. The obviously safer approach of checking the check digit was not merely neglected, but actively forbidden.

lifthrasiir 3y ago
It is possible that a check digit could happen to be incorrect from the beginning. This (and more rarely, an accidental code reuse) does happen fairly commonly with ISBN, so I would expect the same for general UPC/EAN.
efreak 3y ago
Barcodes are entered as text. Older barcode scanners used to plug into either the serial port or the PS2 keyboard port; often they had an inline adapter so you could plug it in between your computer and keyboard. As a checksum, the last digit of the barcode is not part of the data (product number), it's metadata; when the barcode reader beeps, that means it has computed the check digit and it matches the digit on the barcode. The barcode data is sent to the computer, but the check digit is not. The check digit is not in the database. The computer using the UPC leaves it to the barcode reader or human to ensure the input is correct. You'll might also notice that similar barcodes exist in multiple places as well--unopened cases of products might have an identifier that includes the UPC, and so does the price sticker on the shelf. Both of these include more data than just the UPC.

andirk 3y ago

As a grocery checker, I also remember not typing the checksum. It isn't part of the product's ID, but manually typing in probably has a higher chance of error than scanning so what the heck?? Another fun fact: in the intro to The Simpsons, Maggie gets scanned by the clerk as a valid item with a price shown on the register.