Code 39 is an alphanumeric code. Each character is built by 9 elements (5 lines and 4 spaces) where 3 are thick and 6 are thin. This allows the self checking of code 39. Code 39 does not require a build-in check digit. The main advantage is the wider character set.
Code 39 is available with and without a check digit. This check digit is calculated according to Modulo 43.
And here is the code if you use the Type “Code 39 Checksum” (#26) width a check digit calculated according to Modulo 43: