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Gauge R&R study (MSA)

A Gauge R&R study decomposes measurement variation into repeatability (equipment), reproducibility (appraisers) and part-to-part, following the AIAG crossed design.

What is Gauge R&R study (MSA)?

Before trusting a measurement process, quantify how much of the observed variation comes from the gauge itself. In the crossed design every appraiser measures every part at least twice: repeat measurements isolate equipment variation, appraiser differences isolate reproducibility, and what remains is real part-to-part variation.

The AIAG verdict reads %Study Var of Total Gauge R&R: < 10% acceptable, 10–30% marginal, > 30% unacceptable. The number of distinct categories (ndc ≥ 5) checks whether the gauge can actually resolve the parts being measured.

When should I use Gauge R&R study (MSA)?

  • Qualifying a measurement instrument or assay before a capability study.
  • Diagnosing whether measurement error or true process variation dominates.

What data does it need?

Part ID + appraiser/operator + numeric measurement (every appraiser × part cell measured ≥ 2 times).

What does it report?

Variance components (VarComp, %Contribution, StdDev, %Study Var), Total Gauge R&R verdict, ndc.

What does it assume?

  • Crossed balanced design.
  • Parts sampled to span the real process range — a narrow part sample inflates %R&R artificially.

How do I interpret the result?

High repeatability share → fix the instrument; high reproducibility share → train/standardize the appraisers.

See also

References

  • AIAG (2010). Measurement Systems Analysis, 4th ed.
  • Cano, Moguerza & Redchuk (2012). Six Sigma: Statistical Engineering for Process Improvement.