A typical Code 39 bar code is:

Code 39 is a discrete, variable-length symbology. It is self-checking in that a single print defect cannot transpose one character into another valid character.

To calculate the optional checksum digit, follow the following steps.

1. Take the value (0 through 42) of each character in the bar code. The start and stop characters are not included in the checksum calculation.
2. Sum the value of each of the values of each of the characters described in step 1.
3. Divide the result from step 2 by 43.
4. The remainder from the division in step 3 is the checksum character that will be appended to the data message before the stop character.

In the following text, we will discuss the encoding of the bar code by considering that the number "1" represents a "dark" or "bar" section of the bar code whereas a "0" represents a "light" or "space" section of the bar code. Thus the numbers 1101 represents a double-wide bar (11), followed by a single-wide space (0), followed by a single-wide bar (1). This would be printed in the bar code as:

1. A start character - the asterisk (*) character.
2. Any number of characters encoded from the table below.
3. An optional checksum digit calculated as described above and encoded from the table below.
4. A stop character, which is a second asterisk character.

Keep in mind that each character begins and ends with a bar, thus the "bar code encoding" always starts and ends with a "1".

If a Code 39 bar code starts with a space, that bar code will be appended to any previous code 39 bar code in the buffer and the system will wait for additional bar code(s). If a Code 39 bar code doesn't start with a space, the bar code will be appended to any previous code 39 bar codes and the entire message will be delivered to the application.

In other words, if a code 39 bar code has additional bar codes to follow, it must start with a space-if the bar code is the last bar code in the message it must not start with a space.

1. The START character (*): 100101101101.
2. The digit "T": enocded as 101011011001.
3. The digit "E": enocded as 110101100101.
4. The digit "S": enocded as 101101011001.
5. The digit "T": enocded as 101011011001.
6. The digit "8": enocded as 110100101101.
7. The digit "0": enocded as 101001101101.
8. The digit "5": enocded as 110100110101.
9. The digit "2": enocded as 101100101011.
10. The STOP character (*): 100101101101.

NOTE: In the above encoding example note that there is an inter-character space between each character. This is not listed in the list of 10 components, but there is an inter-character space between each character. This inter-character space is represented in the graphic by the white space separating the grey areas.