The difference between reading, grading and verification of two-dimensional codes: three levels of quality control

When implementing a traceability system based on two-dimensional codes such as Data Matrix or QR Codes, it is critical to understand the distinction between reading, grading and verification. These three processes represent progressive levels of quality control, each with specific purposes, instrumentation, and outputs. Confusion between these concepts can lead to poor technology choices and traceability problems throughout the supply chain.

In everyday industrial practice, many practitioners believe that it is sufficient for a code to be “readable” in order to consider it compliant. This view profoundly underestimates the critical issues that can arise at later stages of the product life cycle. A code that is perfectly readable under controlled lighting and positioning conditions may be illegible in other operational situations, compromising the entire traceability chain. This is where grading and, at an even higher level, verification come in.

Code reading: the decoding of data

Reading represents the basic level of interaction with a two-dimensional code. It simply involves decoding the information contained in the code using an industrial scanner, camera, or handheld reader. The goal is to extract the encoded data and make it available for business information systems or process control.

During reading, the system captures the code image, identifies the pattern of the array, and applies decoding algorithms to extract the data string. If the process is successful, the system returns the encoded information. If it fails, it simply reports that the code is not readable. No information is provided on the quality of the markup or the cause of any failure.

The main limitation of read-only lies in its dependence on operating conditions. A code may be perfectly readable under optimal lighting, correct positioning and proper optics, but be unreadable under different conditions. This is critical in applications where the marked component goes through different process steps, is handled in different environments, or must remain readable for years under varying environmental conditions.

Readout finds ideal application in contexts where the immediate goal is decoding data for logistics management or process control, without specific requirements on marking quality. However, relying solely on readout to validate marking carries significant risks of traceability problems in subsequent steps.

Grading: standardized quality assessment

Grading represents a higher level of quality control, based on international regulatory standards. For two-dimensional codes, the reference standards are mainly ISO/IEC 15415 for printed codes and ISO/IEC 29158 (AIM DPM) for codes marked directly on the component through technologies such as laser marking.

During the grading process, the system analyzes specific parameters of code quality according to standardized methodologies. These parameters include contrast between light and dark modules, signal modulation, decodability, grid uniformity, correct quiet zone definition, and other geometric and optical aspects. Each parameter is evaluated and ranked with a score from 0 to 4, where 4 represents the highest quality.

The final result of the grading is an overall grade that summarizes the evaluation of all the parameters analyzed. This grade is typically expressed on an alphabetical scale (A, B, C, D, F) or numerical scale (4.0 to 0.0), where A or 4.0 represents excellence and F or 0.0 indicates a noncompliant code. This rating provides an objective and repeatable indication of marking quality.

Grading requires specific instrumentation equipped with illumination and optics calibrated to specific standards. This instrumentation simulates multiple reading conditions and evaluates the ability of the code to be decoded under different operational scenarios. Unlike simple reading, grading provides predictive information about the readability of the code throughout the supply chain.

The importance of grading emerges particularly in the automotive field, where manufacturers impose stringent requirements on minimum acceptable levels. A code with grading B or better ensures reliable readability even under suboptimal conditions, dramatically reducing the risks of traceability errors or rejects in subsequent assembly or maintenance.

Verification: the highest level of quality control

Verification represents the most advanced and comprehensive level of quality control. It is a process that includes not only grading but also conformance of the code to specific standards required by the industry or application, checking the logical correctness of the coded data, and, in many cases, testing for durability and strength.

During verification, in addition to parametric evaluation according to ISO standards, aspects such as compliance with industry-specific standards (GS1, MIL-STD-130, automotive OEM specifications), correctness of data formatting according to established conventions, presence of all mandatory fields, and validity of coded information against corporate databases are checked.

Verification can also include durability testing to ensure that the code maintains legibility over time, subjected to environmental factors such as temperature, humidity, chemicals or mechanical stress. This is critical for direct part marking (DPM) applications where the component must remain traceable throughout its useful life, which can extend for decades in the case of aerospace or automotive components.

A hallmark of verification is the use of hand-held or laboratory verifiers designed to operate under controlled and constant conditions. These devices ensure calibrated and standardized lighting conditions, eliminating environmental variables that could affect the evaluation. Verification is typically performed in laboratory settings precisely to maintain this tight control over operating conditions.

The output of the verification is not a simple quality grade but a complete conformity outcome (OK/NOK) accompanied by a detail of any nonconformities detected. This level of information allows timely intervention in the marking process to correct specific defects, continuously optimizing the quality of the traceability system.

In industrial processes with critical traceability, such as aerospace, medical, or premium automotive, verification is not only recommended but often a regulatory requirement. Safety-critical components must pass documented verification processes to ensure compliance throughout the life of the product.

Synoptic comparison: reading, grading and verification

The evolution of the market: reading and grading as the de facto standard

In recent years there has been a significant evolution in market demands regarding quality control systems for laser marking. What until a few years ago represented an advanced option reserved for particularly demanding industries has now become a de facto standard in most industrial applications.

Production data clearly show this trend. LASIT produces about 500 laser marking systems per year, and more than80 percent of these systems come with integrated reading and grading systems. Such a high percentage testifies to how the market has realized the importance of implementing quality controls as early as the marking stage, rather than relying on later checks or, worse, discovering readability problems only in the final stages of the supply chain.

Several factors have contributed to this transformation. First, increasingly stringent regulations in industries such as automotive, medical, and aerospace have made grading no longer an option but a requirement. Automotive manufacturers, in particular, specify minimum acceptable levels of grading in technical specifications, making parametric control essential already in production.

Second, the integration of vision systems into marking lines has become more accessible economically and technologically. Hardware components are higher performing and less expensive, while analysis algorithms are faster and more efficient. This has made it possible to implement inline grading without significant impacts on cycle times while maintaining line productivity.

Another crucial aspect is the growing awareness of the economic benefits of integrated quality control. Identifying a nonconforming code immediately after marking allows immediate action to be taken, either through rework of the component or correction of marking parameters. This approach prevents much higher costs that would occur if the problem were identified in the later stages of assembly or, even worse, by the end customer.

Operational experience shows that integrated reading and grading systems not only ensure marking quality but also provide valuable data for continuous process optimization. Statistical analysis of the grades obtained makes it possible to identify drifts in the marking process, anticipate optical wear problems, or detect variations in the quality of the components to be marked.

Practical implementation: which solution for which application

The choice between reading, grading and verification depends fundamentally on the requirements of the application and the level of criticality of traceability. For standard logistics applications where components are read under controlled conditions and there are no specific regulatory requirements, simple reading may still be sufficient, although less and less frequently in modern industrial practice.

When marking must ensure legibility along different process steps or at customers with different instrumentation, grading becomes essential. This level of control is typically implemented inline, with vision systems integrated into laser marking lines that evaluate each code immediately after marking, allowing immediate rejection or rework of nonconforming parts.

Full verification is required in contexts where there are regulatory obligations, stringent contractual requirements, or safety-critical applications. In these cases, in addition to inline inspection with grading, periodic laboratory checks are performed with hand-held verifiers, formally documenting compliance for each batch or for representative samples of production.

Integrating these systems into laser marking processes requires specific technical considerations regarding lighting, camera resolution, periodic instrumentation calibration and data management for complete traceability. More advanced systems allow different levels of control to be configured according to the specific code or end-customer requirements, optimizing cycle times without compromising quality where it is critical.

The current trend is toward implementing grading as a standard, with verification reserved for periodic quality control or for specific certifications. This architecture ensures the best trade-off between widespread quality control, productivity and regulatory compliance.