ISO/IEC 15415 Grading Parameters

  • UEC (Unused Error Correction): This is the percentage of error correction capability that is available for further incorrect modules. The assignment of grade is according to the following table:
UEC % Grade
> 62 A (4.0)
> 50 (but less than 62) B (3.0)
> 37 (but less than 50) C (2.0)
> 25 (but less than 37) D (1.0)
< 25 F (0)
  • SC (Symbol Contrast): This is the difference in reflectivity between the brightest module and the darkest module. The assignment of grade is according to the following table:
SC% Grade
> 70 A (4.0)
> 55 (but less than 70) B (3.0)
> 40 (but less than 55) C (2.0)
> 20 (but less than 40) D (1.0)
< 20 F (0)
  • MOD and RM (Modulation): This is a grade based on the amount of variability in reflectivity of the modules. A multi-step process is used to get the modulation grade. First, the reflectivity of each module is compared to the global threshold and the overall symbol contrast according to the following formula:
MOD = 2 * (abs(R - GT)) / SC

The Global Threshold GT is the midpoint between the reflectance of the brightest module and the reflectance of the darkest module. Next, the grade level for each module is determined from the MOD value according to the following table:

MOD % Grade
> 50 A (4.0)
> 40 (but less than 50) B (3.0)
> 30 (but less than 40) C (2.0)
> 20 (but less than 30) D (1.0)
< 20 F (0)

Finally, the value of the grade for the Modulation parameter will be the highest modulation level for which the modules meeting that level will result in a notional Unused Error Correction grade of that level or higher. The module with the lowest MOD is reported as Contrast Uniformity (CU) in General Characteristics to facilitate conformance testing to the requirements of ISO/IEC 15426-2.

The RM parameter works in a similar way, except that for modules which were corrected as errors by error correction, the MOD% is taken as 0 and counts as F in the final evaluation of the Modulation parameter grade according to the notional Unused Error Correction grade.

  • ANU (Axial Non-uniformity): This is the amount of “out of square” the modules are or in other words, a measure of the overall aspect ratio of the symbol. Note that for rectangular symbols which are supposed to be non-square, the ANU parameter reports the deviation from its “correct” aspect ratio.
ANU % Grade
≤ 6 A (4.0)
< 8 (but more than 6) B (3.0)
< 10 (but more than 8) C (2.0)
< 12 (but more than 10) D (1.0)
> 12 F (0)
  • GNU (Grid Non-uniformity): This is the worst-case distance between the calculated center of a module and the ideal location for the center of the module based on perfectly evenly spaced modules. The calculated center of the module is determined using clock track edges in accordance with the reference decode algorithm. The value is reported as a percentage of a module size.
GNU % Grade
≤ 38 A (4.0)
< 50 (but more than 38) B (3.0)
< 63 (but more than 50) C (2.0)
< 75 (but more than 63) D (1.0)
> 75 F (0)
  • FPD (Fixed Pattern Damage): This is the overall grade for all the fixed pattern components. This grade is equal to the lowest grade of all the components listed below. The following is a list of components of the finder pattern for Data Matrix symbols. For QR Code symbols, the parameters described in ISO 18004 QR Code Grading Parameters are applicable.
  • LLS (Left ‘L’ Side): This is a grade based on imperfections in the left ‘L’ side of the finder pattern. There are two checks required to pass. The first requires gaps to be three modules or less and that gaps are separated by stretches of at least four correct modules. The second assigns a grade based on the overall percentage of correct modules according to the following table:
% of incorrect modules Grade
0 A (4.0)
< 9 (but more than 0) B (3.0)
< 13 (but more than 9) C (2.0)
< 17 (but more than 13) D (1.0)
> 17 F (0)

The grade is the highest modulation level in which the first (gap test) passes and the correct module percentage results in a grade of that level or higher.

  • BLS (Bottom ‘L’ Side): This is a grade based on imperfections in the bottom ‘L’ side of the finder pattern (see Left ‘L’ Side).
  • LQZ (Left Quiet Zone): This is a grade based on imperfections in the quiet zone, which is a one-module area to the left of the left ‘L’ side. The grade is based on the percentage of modules, which are correct using the same grading table as for the ‘L’ sides.
  • BQZ (Bottom Quiet Zone): This is a grade based on imperfections in the quiet zone, which is a one-module area below the bottom ‘L’ side.
  • TQZ (Top Quiet Zone): This is a grade based on imperfections in the quiet zone, which is a one-module area above the top clock track.
    • ULQZ (Upper Left Quiet Zone): This is the top quiet zone above the upper left quadrant (Used only for 2 and 4 quadrant symbols, this is the grade based on the segment of the quiet zone above the top clock track of the left quadrant).
    • URQZ (Upper Right Quiet Zone): This is the top quiet zone above the upper right quadrant (Used only for 2 and 4 quadrant symbols, this is the grade based on the segment of the quiet zone above the top clock track of the right quadrant).

  • RQZ (Right Quiet Zone): This is a grade based on imperfections in the quiet zone, which is a one-module area to the right of the Right Clock Track.

    • RUQZ (Right Quiet Zone to the right of the upper right quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the segment of the quiet zone to the right of the upper right quadrant.
    • RLQZ (Right Quiet Zone to the right of the lower right quadrant): Only for 4 quadrant symbols, this is the grade based on the segment of the quiet zone to the right of the lower left quadrant.

  • TTR (Top Transition Ratio): This is a grade based on imperfections in the top clock track, with relation to its adjoining quiet zone. The ratio is the number of transitions from light to dark or dark to light in the quiet zone divided by the number of transitions in the clock track. Since the number of transitions in the quiet zone should be zero, the ideal value for this parameter is zero. However, a small number of transitions can be tolerated as long as the ratio remains relatively low. As the number of teeth in the clock track increases (larger symbols) more transitions in the quiet zone can be tolerated. Also, more transitions in the clock track (which are really imperfections) will tend to improve this measurement. The grading scheme for this transition ratio is:

    • Transition Ratio % Grade
    < 6 A (4.0)
    < 8 (but more than 6) B (3.0)
    < 10 (but more than 8) C (2.0)
    < 12 (but more than 10) D (1.0)
    > 12 F (0)

    The value of the grade will be the highest modulation level for which the ratio gives a grade from the above table of that modulation level or higher.

    • ULQTTR (Transition ratio for Upper Left Quadrant Top Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper left quadrant. For a 2 quadrant symbol, this will be labeled LQTTR.
    • URQTTR (Transition ratio for Upper Right Quadrant Top Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper right quadrant. For a 2 quadrant symbol this will be labeled RQTTR.
    • LLQTTR (Transition ratio for Lower Left Quadrant Top Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower left quadrant.
    • LRQTTR (Transition ratio for Lower Right Quadrant Top Clock Track): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower right quadrant.

    RTR (Right Transition Ratio): Transition ratio (see Top Transition Ratio) for the right clock track in relation to the right quiet zone

  • .ULQRTR (Transition ratio for Upper Left Quadrant Right Clock Track): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper left quadrant. For a 2 quadrant symbol, this will be labeled LQRTR
    • URQRTR (Transition ratio for Upper Right Quadrant Right Clock Track): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper right quadrant. For 2 quadrant symbols, this will be labeled RQRTR.
    • LLQRTR (Transition ratio for Lower Left Quadrant Right Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower left quadrant.
    • LRQRTR (Transition ratio for Lower Right Quadrant Right Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower right quadrant.
  • TCT (Top Clock Track): This is a grade based on imperfections in the top clock track. Some imperfections in the clock track can be tolerated. However, the rule that must be maintained for a passing grade is that three out of every five modules (on a consecutively rolling window of five modules) must be correct. The value of the grade will be the highest modulation level for which this test passes.
    • ULQTCT (Top Clock Track for Upper Left Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper left quadrant. For 2 quadrant symbols this will be labeled LQTCT.
    • URQTCT (Top Clock Track for Upper Right Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper right quadrant. For 2 quadrant symbols this will be labeled RQTCT.
    • LLQTCT (Top Clock Track for Lower Left Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower left quadrant.
    • LRQTCT (Top Clock Track for Lower Right Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower right quadrant.

  • RCT (Right Clock Track): This is a grade based on imperfection in the right clock track (see Top Clock Track).

    • ULQRCT (Right Clock Track for Upper Left Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper left quadrant. For 2 quadrant symbols, this will be labeled LQRCT.
    • URQRCT (Right Clock Track for Upper Right Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper right quadrant. For 2 quadrant symbols, this will be labeled RQRCT.
    • LLQRCT (Right Clock Track for Lower Left Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower left quadrant.
    • LRQRCT (Right Clock Track for Lower Right Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower right quadrant.

  • AG (Average Grade of Damage across many parts of the Finder Pattern): This is a grade that considers the accumulated effect of damage to several parts of the finder pattern. Five values are averaged together. One of these is the lowest of all the grades associated with all the clock track segments, namely TCT, TTR, TQZ and RCT, RTR, RQZ. The other four are LLS, BLS, LQZ, and BQZ. The average must fall in the range of 0.0 through 4.0 and is given a grade according to the following:

    Ave Grade Grade
    Equals 4.0 A (4.0)
    ≥ 3.5 (but less than 4.0) B (3.0)
    ≥ 3.0 (but lessthan 3.5) C (2.0)
    ≥ 2.5 (but less than 3) D (1.0)
    < 2.5 F (0)
Note: The effect of the AG parameter is to lower the overall grade of symbols, which have several individual parameters at or near the same level. For instance, with enough B grades in individual parameters, the overall grade may come out as a C grade rather than a B.
  • DECODE: Report whether the 2D Symbol was decoded in accordance with the reference decode algorithm with the specified aperture.
    • Note: It is possible for decoded results to be reported, but for a failure to occur when decoding in accordance with the reference decode algorithm. In this case, the DECODE grade will be F (0).

    Contrast Uniformity (CU): This is the value of MOD (modulation) for the worst case module selected from a 2D Matrix symbol. This is useful for process control, as way of measuring the drift in reflectivity consistency, and more importantly for testing conformance to ISO/IEC 15426-2 which requires the modulation of a specific module within a conformance test symbol to be reported. This parameter is not graded, nor listed in the Quality Detail tab. Rather, it is reported in General Characteristics.