A special bar code character or characters which provide a scanner with start and stop reading instructions as well as a way of determining the scanning direction.
A pattern of bars and spaces that provides the scanner with start and stop reading instructions. "*" is specified for CODE39. "A", "B", "C" and "D" exists for CODABAR but not for UPC/EAN and ITF.
A bar code character that provides the scanner with start or stop reading instructions as well as code orientation. The start character is usually at the left-hand end and the stop character at the right-hand corner of a picket-fence oriented code.