For example, if you disable symbologies that you're not using, you can keep an employee's candy bar out of your inventory. If you are making a general-purpose system that needs to read only numbers and uppercase letters, you can use Code 39. If you need numbers only, you should use Interleaved 2 of 5 or Code 128. In any case, avoid symbologies that require reconfiguration of the reader, and your life will be easier. Checksums Checksums are additional characters appended to bar codes to guarantee good reads.
Checksums are necessary on some bar codes that are prone to errors.
For example, Interleaved 2 of 5 is a very dense, numeric-only bar code, but it is prone to substitution errors. You should always use a checksum on this code. Other codes, such as Code 128 and Code 39, are self-checking and seldom require a checksum. Use a checksum to guarantee a good read. Use a checksum to guarantee a good read, and pass the checksum on to the computer system.