A Numeric character set means the symbology can only encode numeric data from 0 through 9. Some additional characters may be encoded which are generally control features of the symbology, such as start/stop characters.

A Alpha-Numeric character set means the symbology can encode the digits 0 through 9 as well as alphabetic characters from A through Z. Again, some additional characters may be encoded as start/stop characters.

A Full ASCII character set is one that allows the encoding of the full ASCII character set. This implies any ASCII character, value 0 through 127, may be encoded by the symbology.

In theory, a numeric character set will produce the smallest barcode whereas a Full ASCII character set will require more physical space to encode the same data. Of course, a Full ASCII symbology gives you more flexibility in encoding more types of information than a numeric symbology.

A discrete symbology is one where each and every character encoded in the symbol may be interpeted individually without respect to the rest of the barcode. Such symbologies have characters that both start and end with a bar. Individual characters are separated by some amount of inter-character spacing. The intercharacter spacing carries no information-the only duty of the intercharacter spacing is to separate the characters.

A continuous symbology is one in which the individual characters of the symbology cannot be interpreted by themselves. This is due to the fact that characters start with a bar and end with a space. The final space is "terminated" by the starting bar of the next character. A character cannot be taken individually since, individually, there is no way to know how wide the last space is without knowing where the next character begins. Continuous symbologies normally implement some kind of special termation bar or termination sequence such that the last space of the last data character is terminated by the termination bar.

In the above example, each character is consists of four bars and four spaces. The last space of character 1 is terminated by the first bar of character 2. The last space of character 2 is terminated by the first bar of character 3. The last space of character 3 is terminated by the first bar of character 4. The last space of character 4 is terminated by the termination bar.

All else being equal, a discrete symbologies require more space to print the same data as a continous code since the discrete symbology "wastes" space in the intercharacter spacing. However, a discrete symbology can generally be printed with less quality-this translates to cheaper printers and more tolerance at scan-time.

Other than the amount of space the two types of symbologies require and the types and quality of hardware used to print them, there is no inherent difference in the security afforded by either type. That is to say, it cannot be said that "continuous symbologies are more reliable ore secure than discrete symbologies"-nor can the reverse be said.

A Two-Width symbology has spaces and bars that are either wide or narrow. This has the benefit of simplicity-once it is determine how wide a "narrow" bar or space is, anything over a certain width can be considered "wide." This allows for a large level of print tolerance in lower-quality printing conditions.

A Multiple-Width symbology is one which has bars and spaces that may be of 3 or more widths. The narrowest bar or space may be X in width, a medium-width space or bar may be 2X in width, and a wide bar may be 3X in width. Since there are more possible combinations available in a multiple-width symbology, data encoding is often more efficient and results in a tighter barcode. Multiple-width symbologies are usually continuous symbologies and are often scanned using edge-to-similar-edge decoding algorithms.

Note that "self-checking" does not mean self-correcting. It simply means that a single printing defect will cause a scan to fail rather than decoding the erroneous read into data which the application assumes to be correct.