1. Study Setup
Cp and Cpk should describe a stable process. This tool estimates short-term sigma from the average moving range of consecutive observations. Pp and Ppk use the overall sample standard deviation.
2. Enter Data
The CSV may contain a header such as Measurement. Non-numeric cells are ignored. Observation order matters because moving ranges use consecutive measurements.
Capability Summary
Cp
—
Potential short-term capability
Cpk
—
Actual short-term capability
Pp
—
Overall performance potential
Ppk
—
Actual overall performance
Descriptive Statistics
Observations
—
Mean
—
Within Sigma
—
MR̄ / 1.128
Overall Sigma
—
Sample standard deviation
| Metric | Value | Meaning |
|---|
Charts
Capability Histogram
Specification limits are shown with vertical lines. The smooth curve represents a fitted normal distribution using the overall mean and standard deviation.
Individuals Control Chart
Control limits use the moving-range estimate of within-process sigma. Points beyond the limits are flagged as potential instability.
Interpretation
Capability indices assume the specification limits are valid customer or engineering requirements and that the underlying process is reasonably stable. A high Cpk does not rescue an unstable process.