01 · Purpose
Why and when to use it
Use it as a simple observed-spread summary or as a component of appropriate subgroup control-chart methods.
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.
- Check units and included observations.
- Identify the minimum and maximum.
- Subtract the minimum from the maximum.
- Report the sample size and period.
- Compare with other spread measures and investigate extreme cases.
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.
| Sample 2, 4, 4, 6, 9 minutes | Result |
|---|---|
| Minimum / maximum | 2 / 9 |
| Range | 9 − 2 = 7 minutes |
04 · Interpretation
What the result tells you
Seven minutes is the distance between the observed extremes. It does not define the range that future observations must fall within.
Completion check: An observed range with coverage and limitations stated.
05 · Judgement
Mistakes and limitations
A single unusual reading can dominate the range. Do not compare ranges from very different sample sizes as if they represented equivalent precision.
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.