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# What are the individual AIM DPM Code Quality metrics?

Code Quality results provide detailed feedback on the quality of a symbol according to the Association for Automatic Identification and Mobility (AIM) standard for 2D Data Matrix symbols. All DataMan verifiers provide an overall grade for each verified symbol as well as the grade for individual metrics, which include:

- Cell Modulation: A measure of readability for the actual mark.

  The grade is a reflection of how close the bright cells and dark cells approach a global threshold for a particular mark, indicating the grey-level separation point between the bright cells and the dark cells of any particular mark.

  A mark generates a low Cell Modulation grade when there is a relatively low confidence in the reader being able to classify individual cells as either bright or dark. The score also takes into consideration the error correction capacity built into the symbol (with larger symbols having more error correction capability). For example, a mark will receive a low Cell Modulation grade but a high Unused Error Correction grade if the majority of cells are on the verge of changing their state but do not actually do so.

- Fixed Pattern Damage: The quality of the finder, clocking, and quiet zone patterns within the mark.

  The reader uses several patterns within each symbol to locate and decode the data it contains. The reader generates the Fixed Pattern Damage grade using the same method as the Cell Modulation score, specifically a measurement of reflectance confidence.

- Reference Decode: An indication of whether the standard 2D Data Matrix algorithm was able to locate and decode this particular mark.

  This metric generates a grade of either A or F.

- Cell Contrast: A measurement of the reflectance difference between the bright cells and the dark cells in the symbol, represented as a percentage of the bright cells mean reflected value.

  The AIM-DPM/ISO/IEC TR 29158 specification requires that the image be adjusted so that the bright cells have a mean reflectance value of 78% of complete saturation.

- Axial Non-Uniformity: A measurement of the symmetry of individual cells within the symbol.

- Unused Error Correction: A measurement for the percentage of code words left in a symbol after correcting for any errors.

  When calculating Unused Error Correction, a code word is considered to be in error if at least one of its cells is on the wrong side of the global threshold. 2D Data Matrix symbols have built-in code redundancy, or the presence of duplicate data content.

  A value of 1.00 means no errors were present in any of the code words.

- Grid Non-Uniformity: A measurement for the amount of placement error for the individual cells from a uniformly spaced grid as measured using the clocking pattern of a symbol.

- Cell Growth: A measurement of the change in cell growth in the horizontal and vertical directions.

  The cell size is measured independently along the horizontal (CGH) and vertical (CGV) clocking patterns of the symbol and reported in physical dimensions.

  This metric is not used for generating the overall Symbol Grade but for process control only, and is available only when you enable code quality grading on the Code Quality task pane.

Note: DM8600