Cp vs Cpk vs Pp vs Ppk: choose the right variation estimate
Worked capability examples explain centering, within-subgroup versus overall spread, and the checks needed before interpreting an index.
Control limits
Statistical boundaries calculated for a control chart under its chosen sampling model.
Control limits help detect variation inconsistent with the chart’s modeled common-cause behavior. They are not product acceptance limits. Chart selection, rational subgrouping, independence and distribution assumptions affect their usefulness. Read the SPC guide before interpreting a point beyond a limit or treating all points inside as proof of capability.
See also: Statistical process control (SPC) · Specification limits · Rational subgroup
Use the concept: Sample mean & standard deviation calculator · Cp, Cpk, Pp & Ppk calculator · Downtime log template
In depth
Statistical process control: control charts that catch drift early
Apply SPC where it works — control chart selection, rational subgrouping, capability indices, and the reaction plans that turn charts into control.
Gauge R&R: how much variation is the gauge?
A gauge R&R study separates measurement error from real part-to-part variation, so you can tell whether a tolerance decision is trustworthy.