<human>:  When I scan a barcode, what is the first thing that is read?
<bot>: The first thing that is read is the check digit. The check digit is a number that is added to the end of the barcode to make sure that the barcode is valid. The check digit is calculated by adding the sum of the digits in the barcode. For example, if the barcode is 123456789, the check digit is 9.