A substitution error is the misreading of a barcode. It occurs when a barcode is damaged or incorrectly printed in such a way that a reader recognizes a valid but incorrect character of the barcode system used and thus replaces (substitutes) the correct character. A check digit calculation (check digit) can generally be used to detect such an incorrect reading. Cf. parity check.

Source: logipedia / Fraunhofer IML