8.12 Measurement System Analysis (MSA / Gauge R&R)

Before measuring parts, we must measure the measurement system. Measurement System Analysis (MSA) determines if the variation in data comes from the part (actual) or the gauge (error).

8.12.1 Gauge R&R (Repeatability & Reproducibility)

• Repeatability (Equipment Variation): Can the same operator using the same gauge measure the same part 10 times and get the same result?
• Reproducibility (Appraiser Variation): Can three different operators measure the same part and get the same result?

8.12.2 AIAG Acceptance Criteria

• < 10% Error: Acceptable. The measurement system is robust.
• 10% – 30% Error: Marginal. May be acceptable based on application importance and cost of gauge. Requires Quality Engineering approval.
• > 30% Error: Unacceptable. The system cannot distinguish between good and bad parts. Data from this tool is invalid. Corrective action (fixture repair, training) is mandatory.

Final Checklist

Metric	Acceptance Limit	Action for Failure
% GRR	< 10% (Green)	Release to Production
% GRR	10-30% (Yellow)	Conditional Release (Monitor)
% GRR	> 30% (Red)	Quarantine Tool / Redesign
ndc	> 5	Increase gauge resolution