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.
Sample standard deviation
A measure of observed spread using squared deviations from the sample mean and an n−1 denominator.
Sample standard deviation has the original measurement unit. Calculating it over all entered observations gives an overall sample estimate; it is not automatically a within-subgroup estimate. It also does not establish independence, normality or control. The sample statistics tool shows count, mean, spread and range with an illustrative example.
See also: Rational subgroup · Process capability
Use the concept: Sample mean & standard deviation calculator · Cp, Cpk, Pp & Ppk calculator · Downtime log template
In depth
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.
Takt time vs cycle time vs lead time: calculate the right clock
A worked shift example separates customer pace, observed process speed and end-to-end delivery time, with practical checks before changing the line.