The MSI/Plessey barcode, also known as just MSI, or Modified Plessey, is a numeric barcode that's used on shelves in supermarkets, as well as warehouses, and other storage facilities, for inventory purposes. The barcode on the shelf can be used to tell you what product goes there, how many units should be there, and other pertinent information. The barcode can be of any length, but the length is usually fixed by the specific application it's being used for.
Specifications: The MSI/Plessey barcode is done in binary format, with black bars being represented as "1" and spaces being represented as "0." All numbers, 0 through 9, are thus represented in binary on the barcode. The code begins with a "guard character," to indicate the start of the barcode, followed by the encoded data. After that is an optional check digit. MSI/Plessey supports several types of check digits, but the most common is Mod-10. The digits are added together in a specific way to get a single digit result. If the result matches the check digit, then the code is correct. After the check digit is another guard character to indicate the end of the code.
Advantages: MSI/Plessey can be of any length, and so can potentially be used to encode large amounts of information.
Disadvantages: It can only encode numbers, not letters. The binary format is also inefficient and prone to errors.