MSI Generator

Plessey-family numeric barcode still used for inventory shelves and library collections.

How MSI is structured

MSI — Modified Plessey — is a numeric-only, variable-length symbology. Each digit is written as a four-bit binary value, and every bit becomes a two-bar group: a zero draws a 100 pattern and a one draws 110, so the symbol is effectively the decimal string dumped as binary with a 110 start pattern and a 1001 stop pattern. The result is a long symbol for its data, which is why MSI survives mainly where the label has room to spare.

MSI check digit

The base MSI symbol carries no check digit at all. The variants add one or two: MSI-10 appends a single mod-10 (Luhn-style) digit, MSI-11 a mod-11 digit, MSI-1010 two mod-10 digits and MSI-1110 a mod-11 digit followed by a mod-10 digit. Choose the variant to match what the reader expects — a symbol with two check digits read by a scanner looking for one will come back with trailing digits.

MSI compared with MSI-10

Code 128 C packs the same digits into roughly a quarter of the width and is readable by every modern scanner, so MSI is a legacy and shelf-label symbology rather than a general one. Against the other Plessey derivatives, MSI's appeal is that the check digit variants can be matched to an existing inventory scheme. Compare the MSI-10 generator page for the same breakdown of structure, check digit and use cases.

Common MSI problems

Letters or separators were entered

MSI is digits only. Strip hyphens and spaces from the payload before generating — a part number formatted for people usually needs a second, numeric key if it has to be carried in an MSI symbol.

The check digit variant does not match the reader

MSI-10, MSI-11, MSI-1010 and MSI-1110 are not interchangeable. A mismatch shows up as data with extra digits or as a rejected scan; confirm which variant the reader profile validates and generate that one.

The symbol is too wide for the shelf label

Four bars per bit makes MSI grow quickly with digit count. Shorten the number, reduce the module width, or move the payload to Code 128 C rather than shrinking the symbol until narrow bars merge.

Where MSI is used

Not sure this is the right symbology? The barcode format guide groups every supported 1D and 2D format by industry with its character set and limits.