Bar Code Symbology
A bar code consists of a number of bars and spaces, each of various widths. In some types, the height of the bar will also vary. These bars and spaces encode a specific amount of information. They are used to provide information automatically when scanned, which eliminates having to enter the information by hand. Information is automatically gathered when the bar code is scanned, making it a much faster and a less expensive way to retrieve information. The scanned information is entered without entry errors, which also makes it a more accurate way of entering information.
Because of the special needs of different industries, there have been a number of different types of bar codes developed. The different bar code languages are known as symbologies. Listed below are some of the commonly used symbologies with a brief explanation of each.
Code 39 is the most popular bar code symbology used for ID, inventory, tracking and labeling.
- It can be read by most types of scanners.
- Characters available for encoding include uppercase letters and numbers.
- It can be printed in a wide variety of sizes and dimensions.
- It is self checking but when additional security is required, a check character is an option.
Postnet bar codes are used to encode the zip codes on mail for the Postal Service. The bar coded mail is what allows the routing of mail quickly and accurately.
- Height of bars alternates rather than the width.
- Each number is represented by 5 bars.
- Can be used on 5-digit zip codes, 9-digit zip 4, and the new 11-digit Deliver Point bar code.
Self Checking: This is when a bar code symbology is designed to check itself so that, when read by the scanner, one character is not interpreted as another character. When scanned, all characters are added up and a calculation is made to verify the number. This calculation differs for different types of bar codes. If the resulting calculation is incorrect for that bar code, the bar code reading is rejected.
UPC bar codes are used by the grocery and retail industries. Supersets to UPC are EAN, Jan, Bookland and ISSN bar codes. EAN bar codes are used in Europe and JAN bar codes are used in Japan. Bookland bar codes are used on books and ISSN bar codes are used on magazines.
The number of the item and its price are not actually in the bar code. When the UPC bar code is scanned it pulls out information from an inventory database. This is how the registers know the item name and price. When prices change, they are changed in the database, otherwise each item affected by the price change would have to have its bar code replaced.
The UPC Symbol is numeric only; it is made up of the following:
- The number system, single digit in lower left corner.
- A 5 digit manufacturer number on the left, assigned by the Uniform Code Council.
- A 5 digit product number on the right that identifies the product, assigned by the manufacturer.
- A check character found in the lower right hand corner.
- There is an option to add supplemental 2 or 5 digit numbers that can be placed to the right of the main symbol.
- This gives additional encoding options.
- There are human readable digits below the UPC code and above the supplemental code.
Check Character: A check digit that is used for error checking purposes. Code 39, UPC, 2 of 5 and Code 128 are some of the symbologies that can have a check character.
This type of bar code is used mostly in the shipping industry and on labels. This code is variable in length, alphanumeric, and continuous where all spaces are part of the characters. Each character consists of three bars and three spaces.
- This is a very compact, high density symbol.
- Because of its high density it makes very efficient use of space.
- Encoded characters include numbers, letters and special characters.
- This bar code contains a Check Character.
Interleaved 2 of 5
Most popular bar code used by shipping and warehouse industries; also used in the medical field.
- The code is variable in length and is numeric only.
- It is also a continuous symbology.
- Each character consists of 5 bars and 5 spaces.
- Each character encodes 2 digits.
- The bars encode the odd digits, and the spaces encode the even digits.
- This is the highest density symbology for numeric data.
- It is a self checking code but the use of a check character is optional if additional security is necessary.
Some of the characters in Interleaved 2 of 5 can be interpreted as start and stop patterns when a partial scan is made. Adding these bars would cause an invalid read if a partial scan occurred. Otherwise, the partial scan may read as valid even though it is actually invalid.
Other Bar code Symbologies Used in Specialized Markets
- Codabar - Used by FedEx, by libraries, and blood banks.
- MSI - Used on self pricing labels in retail stores.
- Code 93 - Used on small electronic components.
2D Bar Codes
2D (two dimensional) bar codes are a new technology in bar coding that will probably gain popularity in the future. The bar codes described above are traditional one dimensional bar codes which limits the amount of data capacity they have available. 2D bar codes have the capability of storing large amounts of data. These bar codes are not made up of all bars and spaces, they are a non-linear symbology that is very high density. Some advantages and disadvantages of 2D bar codes are listed below.
Advantages: They have the ability to store large amounts of data in a small space.
2D bar codes can encode photos, images, biometric characteristics (such as fingerprinting) and other data.
Entire records can be stored on a card rather than being a pointer to a external database.
Disadvantages: The software is more expensive than one dimensional bar codes but will become more affordable as the technology gains popularity.
A special scanner is needed to read the 2D bar code symbologies.
Other Scanned Symbologies
There are other scanned symbologies used in addition to bar code symbologies. Some are used with the bar codes and some are used independent of the bar code. These are OCR (Optical Character Recognition) Symbologies.
- OCR-A - Used on book covers to format the ISBN number.
- OCR-B - Used for the human-readable digits under the UPC, EAN, JAN, Bookland and ISSN bar codes.
- MICR - MICR (Magnetic Ink Character Recognition) is the use of a special font for the numbers on the bottom of a check. It is printed in a special magnetic ink or toner which allows it to be scanned by the bank's processing equipment.
Choosing the Right Symbology
The final use of the bar code is usually what determines which symbology should be used. For example, if the product will be sold in a supermarket, the UPC symbology must be used. Products sent to the U.S. Department of Defense must be coded with Code 39 symbology. If the bar code is for internal use and there are no predetermined factors, you should consider such things as the amount of space available for the bar code, the type of data to be encoded currently and in the future, and the type of scanning equipment that will be used.