Code 39

Code 39 is a variable length code whose maximum length depends upon the reading equipment used. Code 39 is self-checking and does not require a check digit in normal commercial and industrial applications. Code 39 characters are discrete with a range of intercharacter gaps permitted. Code 39 is bidirectional, meaning it can be scanned from left to right or right to left. High density Code 39 is 9.4 characters per inch, but densities as low as 1.4 characters per inch are included in the recommended practices of corrugated containers. A unique character, conventionally interpreted as an asterisk (*), is used exclusively for both a start and stop character.

A Code 39 symbol consists of a leading quiet zone, a start character, appropriate data characters, a stop character, and a trailing quiet zone. In Code 39, wide elements are considered multiples of the narrow elements. The minimum nominal wide-to-narrow ratio is 2:1 and the maximum is 3:1. The best first pass read rates and substitution error rates can be expected when the wide-to-narrow ratio is at its maximum of 3:1.