01 · Purpose
Why and when to use it
Use it when different people measure a range of items and measurement variation could affect decisions.
Who takes part?
The measurement owner works with people who understand the process and the recorded data. Statistical or measurement-system decisions should involve someone able to check the assumptions and study design.
02 · Application
How to apply it
Start with an agreed measurement purpose, explicit units and trustworthy observations. Identify missing cases and assumptions before calculating.
- Select parts spanning the relevant operating variation.
- Choose representative operators and independent repeat measurements.
- Randomise order and blind prior readings in a crossed study where each operator can measure each part.
- Use a suitable variance-components analysis; inspect operator-by-part interaction.
- Report measurement variation with its denominator and improve the system where needed.
03 · Example
A worked measurement example
Original fictional teaching example. Small datasets illustrate the method; they are not proposed as sufficient study sizes. Supplied parameters are assumptions, not estimates from a real process.
| Variance component | Illustrative value (g²) |
|---|---|
| Repeatability | 0.04 |
| Operator-related reproducibility, combined | 0.05 |
| Total Gage R&R | 0.04 + 0.05 = 0.09; SD = 0.30 g |
| Part-to-part | 0.91 |
| Total observed variance | 1.00; % variance contribution from R&R = 9%; % study variation = 30% |
04 · Interpretation
What the result tells you
Nine percent of variance and thirty percent of standard-deviation-based study variation describe the same example with different denominators. Label the metric explicitly. The supplied component values are illustrative, not fitted from a dataset here.
Completion check: A documented continuous Gage R&R study with components, metric definitions and decisions.
05 · Judgement
Mistakes and limitations
A crossed design is unsuitable if measuring destroys the part; consider a justified nested or destructive-test design. Study parts must not be chosen merely to inflate process spread and make the gage look better.
07 · Reading
Sources and further reading
The tool list follows the accepted LeanTrainingLab overview and its reference to Six Sigma+Lean Toolset, second edition (Lunau, editor; Springer, 2013). The book chapters were not available for direct review during this build. Explanations, examples and worksheets are original teaching material. Further reading supplies professional background; local conventions are stated explicitly.