Every product is assigned a unique thirteen-digit number (ten digits for the product itself, a check digit, and a couple of flag characters to indicate which organization assigned the number).

Contained within those seemingly random codes are – you guessed it – check digits: “find an object with a 13-digit barcode.

Barcodes became a thing in 1974. The 12-digit code helped track inventory and provided info on the product. QR codes were invented 20 years later in 1994.

According to Biz Fluent, the first digit of a 12-digit barcode identifies the numbering system, and the next five digits identify the manufacturer. The last five digits identify the product.

The check digit or checksum is determined by a four-step equation the starts by adding the digits in every odd-numbered position.

The final digit is what’s called a check digit, which the computer uses to verify that all the other numbers in the code have been scanned or entered correctly.

For the most common key, the serialized GTIN-96—or SGTIN-96—those 96 bits contain some simple reader instructions, followed by the GTIN (13 decimal digits without its bar-code check digit, which is ...

A simple example illustrates the idea: if the information digits are added together, then the check-digit is chosen so that the total of all 13 digits is a multiple of 10.