2026.03.31 | MiDFUN Editorial Team
About This Article
MSA (Measurement System Analysis) is a set of statistical methods used to evaluate the accuracy, precision, and stability of a measurement system and to confirm whether the measurement data is reliable. MSA is one of the five AIAG core tools and a mandatory requirement of the IATF 16949 quality management system. The MiDFUN MSA system provides complete GR&R analysis, instrument calibration management, and reporting features to help manufacturers implement measurement quality management.
What Is MSA (Measurement System Analysis)?
The full name of MSA is Measurement System Analysis. According to the definition in the AIAG MSA Reference Manual (Fourth Edition), MSA is a set of statistical methods for analyzing the variation of a measurement system. The "measurement system" referred to here is not just the measuring instrument, but the whole system covering all of the following elements:
- People (Appraiser): the personnel who operate the measuring instrument
- Instrument (Gage): the measuring equipment and tools
- Method: the standard operating procedure for measurement
- Environment: environmental conditions such as temperature and humidity
- Part: the object being measured
The core purpose of MSA is to answer one key question: can our measurement data actually be trusted? If the measurement system itself has excessive variation, then the quality judgments and process improvement decisions made based on that data may all be wrong. Therefore, before performing any quality data analysis, you must first confirm how reliable the measurement system is.
The Five MSA Analyses
The AIAG MSA manual breaks down measurement system variation into five aspects, each corresponding to a statistical analysis method:
| Analysis Item | English | What It Evaluates |
|---|---|---|
| Bias | Bias | The difference between the measurement average and the true value (reference value) |
| Linearity | Linearity | Whether bias changes with the magnitude of the measured value across the measurement range |
| Stability | Stability | Whether the measurement results stay consistent as the measurement system ages over time |
| Repeatability | Repeatability | The degree of variation when the same person uses the same instrument to measure the same part multiple times |
| Reproducibility | Reproducibility | The difference in measurement results when different people measure the same part |
Of these, Repeatability and Reproducibility together are called GR&R (Gage Repeatability & Reproducibility), the most widely used analysis item in MSA and the one most often required in customer audits. Bias, linearity, and stability are "location" characteristics of the measurement system, typically performed after instrument calibration or during periodic evaluations.
How Do You Interpret GR&R (Gage R&R)?
The result of GR&R analysis is expressed as %GR&R, representing the proportion of measurement system variation relative to the total variation (or tolerance). According to the acceptance criteria in the AIAG MSA manual:
| %GR&R Range | Result | Explanation |
|---|---|---|
| < 10% | Acceptable | The measurement system has small variation and reliable data, suitable for process control and analysis |
| 10% ~ 30% | Conditionally Acceptable | Whether to improve should be evaluated comprehensively based on the importance of the application, the cost of the gage, and repair expenses |
| > 30% | Unacceptable | The measurement system variation is too large; the cause must be found and improved, and GR&R must be re-run after improvement |
In addition to %GR&R, another important indicator is the Number of Distinct Categories (ndc). The ndc represents the number of part groups the measurement system can effectively distinguish. AIAG recommends that ndc should be greater than or equal to 5, indicating that the measurement system has sufficient discriminating power. If ndc is below 5, the measurement system's usefulness is still insufficient even if %GR&R is within the acceptable range.
Common methods for GR&R analysis include the Average & Range Method and the ANOVA Method (Analysis of Variance). The ANOVA method can additionally break out the interaction effect between operators and parts, and is currently the more recommended analysis method. The MiDFUN MSA system supports both crossed and nested GR&R analysis and automatically calculates %GR&R and ndc.
MSA Requirements in IATF 16949
The IATF 16949 quality management system lists MSA as a mandatory requirement, with related clauses spanning multiple aspects:
- Clause 7.1.5.1.1 (Measurement System Analysis): requires statistical studies to be conducted for each measurement system referenced in the Control Plan, with analysis methods conforming to the AIAG MSA manual or a customer-specified reference manual.
- Clause 7.1.5.2.1 (Calibration/Verification Records): requires records of calibration/verification activities to be established for all gages, measuring, and test equipment, including equipment identification, calibration date, calibration results, and more.
- Clause 8.3.5.2 (Manufacturing Process Design Output): in the APQP (Advanced Product Quality Planning) process, the MSA plan is one of the required outputs of manufacturing process design.
- Clause 10.2.3 (Problem Solving): during the handling of nonconformities, the capability of the relevant measurement system must be confirmed as sufficient, which means MSA data evidence is needed.
In practice, the GR&R report is what is most often requested during customer audits. If you cannot provide a passing MSA report, it may lead to an audit Non-Conformity, directly affecting supplier ratings and order acquisition. The Chanhe Hardware MSA implementation case is an example of building a complete instrument management system to meet customer audit requirements.
The Relationship Between MSA and SPC
SPC (Statistical Process Control) is a quality tool that uses control charts to monitor process stability. The variation shown on an SPC control chart can be broken down into two sources: the variation of the process itself and the variation of the measurement system.
If the measurement system's share of variation is too high (for example, %GR&R > 30%), a large part of the fluctuation seen on the SPC control chart is actually measurement noise rather than true process variation. This leads to two risks:
- False Alarm: the process is normal but measurement noise triggers an out-of-control alarm, wasting effort investigating problems that do not exist
- Missed Signal: a genuine process shift is masked by measurement noise, allowing defective products to slip out
In addition, the calculated result of the standard deviation (Sigma) is also inflated by the measurement system's variation, causing process capability indices such as Cpk to be underestimated. Therefore, both the AIAG manual and IATF 16949 explicitly require: do MSA first, confirm the measurement system is acceptable, and then perform SPC analysis. This is the basic order of quality management.
Frequently Asked Questions (FAQ)
Q1: What is MSA (Measurement System Analysis)?
MSA (Measurement System Analysis) is a set of statistical methods used to evaluate the accuracy, precision, and stability of a measurement system. The object of analysis covers all factors that affect the measurement result, including people, instruments, methods, and the environment. MSA is one of the five AIAG core tools and a mandatory requirement of the IATF 16949 quality management system.
Q2: What is GR&R? How do you decide whether a measurement system is acceptable?
GR&R (Gage Repeatability and Reproducibility) is the most commonly used method in measurement system analysis, used to quantify the variation of repeatability and reproducibility. Acceptance criteria: %GR&R < 10% is acceptable; 10%~30% is conditionally acceptable; > 30% is unacceptable and must be improved. In addition, the Number of Distinct Categories (ndc) should be ≥ 5, indicating that the measurement system has sufficient discriminating power.
Q3: How is MSA different from instrument calibration?
Calibration compares the readings of a measuring instrument against a standard to confirm whether they fall within the allowable error range; it is a check of whether the instrument is right or wrong. MSA evaluates the degree of variation of the entire measurement system (including operator handling and environmental conditions); it is an evaluation of how good the system is. Passing calibration is a basic prerequisite; passing MSA is what proves how reliable the measurement data is.
Q4: Why do MSA before SPC?
The variation on an SPC control chart comes from two parts: process variation and measurement system variation. If the measurement system variation is too large, the fluctuation shown on the SPC control chart may be mostly measurement noise, leading to wrong judgments. Therefore, you must first use MSA to confirm the measurement system is acceptable (%GR&R < 10%) before SPC analysis is meaningful.
Q5: What features does the MiDFUN MSA system provide?
The MiDFUN MSA system provides GR&R analysis (crossed and nested methods), bias/linearity/stability analysis, instrument calibration scheduling and due-date reminders, electronic management of calibration records, instrument history tracking, and report output that complies with IATF 16949 and the AIAG MSA manual requirements. The system also supports integration with the SPC system, achieving unified management of measurement quality and process quality.
Learn About the MiDFUN MSA System
Complete GR&R analysis, instrument calibration management, and MSA reporting features to help you meet IATF 16949 audit requirements.
Copyright © 2026 MiDFUN Co., Ltd. Some rights reserved
Author: Pei-Chi Chiu. First published: 2026-03-31. Type: Quality Management Column
Original link: https://www.midfun.com.tw/qc/glossary-msa-measurement-system-analysis/
This work is released under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). You are welcome to share it freely, provided that you attribute the original author, include the original link, do not use it commercially, and do not modify the content.
Suggested citation: Pei-Chi Chiu (2026). "What Is MSA (Measurement System Analysis)? GR&R Acceptance Criteria and IATF 16949 Requirements." MiDFUN Quality Management Column.
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