MSI Plessey (Mod 11)
MSI with a Mod 11 check digit — the weighting scheme borrowed from ISBN, for stronger single-digit error detection.
MSI Plessey (Mod 11) Specification
| Character set | Digits 0-9 only (check digit may render as X) |
| Data length | Variable; typically 4-12 digits |
| Check digit | One Mod 11 weighted check digit (may be X) |
| Density | ≈9-13 digits per inch depending on X |
| Module width (X-dimension) | 0.25-0.50 mm typical |
| Print ratio | Four binary-weighted bars per digit |
| Magnification | Scales with X-dimension |
| Quiet zone | 10X on each side |
| Standard | No ISO standard; vendor conventions |
| Origin | MSI Data Corporation, 1972 |
| Sample data | 1234567 |
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What Is MSI Plessey (Mod 11)?
MSI Mod 11 applies the classic weighted Mod 11 algorithm as MSI's check digit: digits are multiplied by alternating weights of 2 and 3 (or a cascading 2,3,4... scheme depending on the variant), summed, and the complement modulo 11 becomes the check digit — which may therefore be the letter X when the remainder is 10.
The weighting structure catches transposition errors (adjacent swapped digits) that plain Mod 10 can miss, which matters in inventory counts and shelf-location numbering. Warehouse management systems of the 1980s standardized their own Mod 11 variants, so field deployments differ subtly in weighting direction; matching the exact legacy scheme is the main integration risk.
Common Applications
- Legacy warehouse systems requiring Mod 11 validation
- Shelf and bin labels with transposition protection
- Interfacing with WMS platforms standardized on Mod 11
Related Barcode Types
MSI Plessey (Mod 11) FAQ
Why can the MSI Mod 11 check digit be an X?
Modulo 11 arithmetic can yield a remainder of 10, which has no single digit. Convention writes it as X — the same trick ISBN used for decades. Scanners transmit the X, so receiving systems should treat the check field as alphanumeric.
What error does Mod 11 catch that Mod 10 misses?
Digit transposition — 1234 scanned as 1243 — fails the alternating-weight check but can pass a Luhn check depending on positions. Since shelf-location numbering is exactly the use case where humans transpose digits, legacy WMS vendors often picked Mod 11 for it.