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Gauge R & R Study

Gage Repeatability and Reproducibility (Gage R & R) is a methodology used to

define the amount of variation in the measurement data due to the measurement system.

The two most widely accepted methods for calculating Gage Repeatability and Reproducibility

The Average and Range Method ( X bar and R)

(Part to part, Repeatability, Reproducibility ) Crossed method only

The ANOVA method (Analysis of Variance) Method

(Repeatability, operators, operator by part) More accurate (Crossed, Nested, Expanded)

For data collection selection using these three analysis for gauge R&R study.

1) Crossed 2) Nested 3) expanded

Expanded

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Measuring system variation

Due to Inspector

Variation (Width Variation)

(PRECISION)

Due to equipment

Variation (Location Variation)

(ACCURACY)

Repeatability

Reproducibility

Accuracy

(Bias)

Linearity

Stability

(consistency)

Variation due to gauge

Operator

Operator by Part

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Attribute gauge: A different type of instrument that gives a binary pass/fail measurement result.

Example : Examples of attribute gages include go/no-go plug gages, slip gages and

many visual inspection processes.

Variable Gage : Variable gages are those that provide actual measurement deviations.

In this way, they provide the data a shop needs to make decisions about process trends,

to diagnose manufacturing issues and to learn a little about the form of a part.

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Gauge R&R study

Attribute gauge

Variable gauge

Repeatability

Reproducibility

Bias/

Accuracy

Linearity

Stability

Repeatability

Reproducibility

Bias/

Accuracy

Linearity

Stability

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Acceptance criteria for Variable gauge: According to the Automotive Industry Action

group (AIAG) measurement system assessment using %GRR

Acceptance criteria for Atribute gauge:

Decision	Effectiveness	Miss Rate	False Alarm Rate	Effectiveness Rate
Acceptable for the appraiser	> 90%	< 2%	< 5%	>=90
Marginally acceptable for the appraiser	80% to 90%	2% to 5%	5%to 10%	>=80<90
Unacceptable for the appraiser	< 80%	> 5%	> 10%	<80

NDC (number of distinct categories) = > 5

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Calculate the number of distinct categories (NDC) for Variable gauge :

According to Automotive Industry Action Group (AIAG), the number of distinct categories

should be greater than 5 for an adequate measuring system

Number of distinct categories =(Standard deviations for parts / standard deviation for gage) * √2

The number of distinct categories is a metric that is used in gage R&R studies to identify a

measurement system's ability to detect a difference in the measured characteristic.