Frequently Asked Questions

Common questions about MSA, GRR, and our tool

MSA (Measurement System Analysis) is the broader methodology that evaluates the entire measurement system, including:

  • Gage R&R (Repeatability & Reproducibility)
  • Bias studies
  • Linearity studies
  • Stability studies

GRR (Gage Repeatability & Reproducibility) is a specific component of MSA that focuses on:

  • Repeatability: Variation when the same operator measures the same part multiple times
  • Reproducibility: Variation between different operators measuring the same part
Think of it this way: MSA is the complete health checkup, while GRR is checking blood pressure and heart rate.

Parts
  • Minimum: 5 parts (for preliminary studies)
  • Recommended: 10 parts
  • Optimal: 10-20 parts

Part Selection Tips:

  • Span the expected measurement range
  • Include parts near specification limits
  • Use production-representative parts
Operators
  • Minimum: 2 operators
  • Recommended: 3 operators
  • Maximum: 4-5 operators (diminishing returns)

Operator Selection Tips:

  • Include typical production operators
  • Ensure all are trained on the procedure
  • Mix experience levels if possible
Our Tool Helps: Use our MSA-GRR Sample Selection Tool to optimize part selection for your study!

%GRR represents the percentage of total observed variation that is due to the measurement system (rather than actual part differences).

%GRR Range Classification Recommendation Typical Action
< 10% Excellent Acceptable for all applications Approve for use
10% - 30% Marginal May be acceptable depending on application Evaluate criticality, consider improvement
> 30% Unacceptable Measurement system needs improvement Do not use, implement improvements
Important: These are general guidelines. Some applications may require stricter criteria (e.g., <5% for critical safety measurements).

NDC (Number of Distinct Categories) represents how many distinct groups the measurement system can reliably distinguish.

NDC Interpretation:
  • NDC ≥ 5: Acceptable discrimination
  • NDC = 3-4: Marginal discrimination
  • NDC < 3: Poor discrimination
Formula:
NDC = 1.41 × (σpart / σGRR)
Practical Meaning:

If NDC = 5, your measurement system can reliably distinguish between 5 different groups of parts.

Example: If you're measuring parts with a tolerance of ±0.005", and NDC = 5, you can reliably detect differences of about 0.002" between parts.

Our MSA-GRR Sample Selection Tool uses advanced optimization algorithms to select the best units for your GRR study.

How it works:
  1. Data Analysis: Analyzes your uploaded measurement data
  2. Parameter Detection: Automatically identifies valid measurement parameters
  3. Optimization: Uses statistical algorithms to select units that:
    • Span the measurement range effectively
    • Maximize discrimination capability
    • Represent typical process variation
  4. Output Generation: Creates properly formatted GRR worksheets
Benefits:
  • Saves time in part selection
  • Improves study effectiveness
  • Reduces bias in selection
  • Provides consistent methodology

Supported Formats:
  • CSV files (.csv)
  • Excel files (.xlsx)
  • Maximum file size: 16MB
Required Structure:
  • First column: Unit/Part identifiers
  • Subsequent columns: Measurement data
  • Numeric data for measurements
  • Headers in first row (recommended)
Example Data:
Unit_ID Length Width Height
Unit_00110.255.122.98
Unit_00210.315.083.02
Unit_00310.185.152.95
Detailed Format Guide

High %GRR indicates your measurement system contributes too much variation. Here's a systematic approach to improvement:

High Repeatability (%EV):

Equipment-related issues

  • Calibrate or repair the gage
  • Improve gage resolution
  • Control environmental conditions
  • Improve part fixturing/clamping
  • Reduce vibration and noise
  • Consider different measurement method
  • Check for worn measurement surfaces
High Reproducibility (%AV):

Operator-related issues

  • Improve operator training
  • Standardize measurement procedure
  • Improve work instructions
  • Add measurement aids/fixtures
  • Reduce operator subjectivity
  • Consider automation
  • Ensure consistent setup procedures
Investigation Steps:
  1. Determine if %EV or %AV is the main contributor
  2. Review the measurement procedure
  3. Check equipment calibration and condition
  4. Observe operators during measurement
  5. Implement targeted improvements
  6. Re-run the GRR study to verify improvement

Automotive Industry:
  • AIAG MSA Manual: Primary reference for automotive MSA
  • ISO/TS 16949: Quality management for automotive
  • VDA Volume 5: German automotive MSA standard
General Standards:
  • ISO 9001: General quality management requirements
  • ISO 10012: Measurement management systems
  • ISO/IEC 17025: Testing and calibration laboratories
Medical Device:
  • ISO 13485: Medical device quality management
  • FDA 21 CFR Part 820: US medical device regulations
Aerospace:
  • AS9100: Aerospace quality management
  • AS9102: First article inspection
Laboratory:
  • ASTM E691: Interlaboratory studies
  • ISO 5725: Accuracy and precision
Note: Always check with your specific industry and customer requirements, as MSA criteria may vary based on application criticality.

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