How to Recognize a Code 128 Barcode

Code 128 barcodes all have the same stop bar pattern on the right side of the bar code symbol. The three code sets all have different start bars on the right but share the same Code 128 stop bar pattern.

The check digit is calculated by adding the value of the start character to each character's value, multiplied by its ordinal position in the string. The subtotal is divided by 103. The check digit is the character associated with the remainder.

This short video illustrates this: