01 · Purpose
Why and when to use it
Use it to inspect clustering, gaps and unusual values before calculating summaries.
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 the variable and its unit.
- Choose a numerical scale covering the observations.
- Plot one dot per value; stack duplicates.
- Use separate rows for groups if a comparison is needed.
- Describe visible features and investigate unusual observations.
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.
| Packing time (minutes) | Number of observations |
|---|---|
| 2 | 1 |
| 4 | 2 |
| 6 | 1 |
| 9 | 1 |
04 · Interpretation
What the result tells you
For 2, 4, 4, 6 and 9 minutes, the duplicate at 4 is visible and 9 is the largest value. A larger value is not automatically erroneous or a special cause.
Completion check: A display retaining each observation’s value and frequency.
05 · Judgement
Mistakes and limitations
Many observations can overcrowd the chart. Do not infer time order from a value-axis plot; use a run chart for that purpose.
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.