Understanding Verification Grades
Marking a code that “looks good” isn’t enough. Industrial traceability requires verified codes — codes that have been measured against an objective standard and assigned a grade.
ISO/IEC 15415: The 2D Code Grading Standard
ISO/IEC 15415 evaluates 2D codes on 9 parameters, each scored from 0–4 (A–F):
| Grade | Score | Meaning |
|---|---|---|
| A | 4.0 | Excellent — highest readability |
| B | 3.0 | Good — reliable scanning |
| C | 2.0 | Acceptable — meets most industry requirements |
| D | 1.0 | Marginal — may fail on some readers |
| F | 0.0 | Fail — unreadable or unreliable |
The overall grade is the lowest individual parameter grade. One failing parameter drags the entire code down to that grade.
The 9 Grading Parameters
| Parameter | What It Measures | Common Laser Marking Issue |
|---|---|---|
| Decode | Can the code be read at all? | Insufficient contrast, damaged finder pattern |
| Contrast | Difference between light and dark cells | Low power, wrong marking method |
| Modulation | Consistency of contrast across the code | Uneven marking depth, thermal gradients |
| Fixed Pattern Damage | Integrity of finder/timing patterns | Over-marking distorts the L-finder pattern |
| Grid Non-Uniformity | Accuracy of the cell grid alignment | Galvo calibration drift |
| Axial Non-Uniformity | Consistency of cell spacing in X vs Y | Galvo axis imbalance |
| Unused Error Correction | Remaining error correction capacity | Cell damage reduces ECC margin |
| Angle of Distortion | Square-ness of the code | Skewed galvo or misaligned workpiece |
| Print Growth | Cell size accuracy (over/under marking) | Power too high = cell spreading |
For Direct Part Marking: AIM DPM-1
When laser marking directly on metal or plastic (rather than printing on a label), the verification standard is AIM DPM-1 (also referenced as ISO/IEC TR 29158). This standard adjusts the grading criteria to account for the unique challenges of DPM:
- Reflective metal surfaces
- Curved or uneven marking surfaces
- Lower contrast than printed labels
- Surface texture effects
Most industrial customers require Grade C or above under AIM DPM-1. Some high-reliability applications (aerospace, medical) require Grade B.
