Sigma overall

long-term standard deviation

s = √(Σ(x − x̄)² / (n − 1))

The ordinary sample standard deviation of all values. It contains short-term noise plus all shifts and drift and is used for Pp and Ppk.

Calculate it

Process Capability & Control Charts: Cp, Cpk, Pp, Ppk, PPM and confidence intervals with X-bar/R, X-bar/S or I-MR charts and all 8 Nelson rules.