MSI Plessey (Mod 10)
A digits-only inventory barcode with a single Mod 10 check digit, descended from the Plessey code.
MSI Plessey (Mod 10) Specification
| Character set | Digits 0-9 only |
| Data length | Variable; typically 4-12 digits |
| Check digit | One Mod 10 (Luhn-style) check digit appended |
| Density | ≈9-13 digits per inch depending on X and bar width |
| Module width (X-dimension) | 0.25-0.50 mm typical |
| Print ratio | Each digit is four binary-weighted bars (narrow/wide by position, not a fixed ratio) |
| Magnification | Scales with X-dimension |
| Quiet zone | 10X on each side |
| Standard | No ISO standard; AIM MSI specification and vendor conventions |
| Origin | MSI Data Corporation (adapting Plessey Company code), 1972 |
| Sample data | 1234567 |
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What Is MSI Plessey (Mod 10)?
MSI (Modified Plessey, sometimes MSI Plessey) adapts the 1970s Plessey Company code into a digits-only symbology popularized by MSI Data Corporation for inventory control. Each digit is four bars long with a fixed binary-weighted pattern — the same pulse-position idea as the original Plessey code, but restricted to the ten digits, which simplifies decoding and printing.
MSI carries no ISO standard; it survives on pure installed base — warehouse shelf labels, library circulation, and especially video-rental and retail inventory systems of the 1980s-90s whose scanners and databases still run. Modern systems choose it only for compatibility. The Mod 10 variant appends one check digit using the same Luhn-family algorithm as EAN/UPC, giving basic error detection for scanned inventory counts.
Common Applications
- Warehouse shelf and bin location labels
- Library and media circulation (legacy)
- Retail inventory control systems (legacy)
Related Barcode Types
MSI with a Mod 11 check digit — the weighting scheme borrowed from ISBN, for stronger single-digit error detection.
MSI with two chained Mod 10 check digits — double validation for high-volume scanning.
A self-checking numeric barcode with start/stop letters, historically used by libraries and blood banks.
MSI Plessey (Mod 10) FAQ
How is the MSI Mod 10 check digit computed?
Take the data digits, double every second digit from the right, split any two-digit products into their digits, sum everything, and take the 10's complement of the units digit. It is the familiar Luhn algorithm. The generator appends the result; scanners verify and strip it.
Should a new system still choose MSI?
Only to talk to existing MSI hardware or databases. MSI has no ISO standard, no alphanumeric support, and weaker self-checking than Code 128, which matches or beats it in every technical dimension. MSI persists because replacing working inventory infrastructure costs more than the barcode format matters.