Sigma within

short-term standard deviation

σ = R̄ / d₂, S̄ / c₄ or MR̄ / 1.128

The standard deviation estimated from the variation inside rational subgroups. It represents the inherent, short-term noise of the process and is used for Cp, Cpk and the control limits.

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.

Related terms

• Sigma overall: long-term standard deviation
• d₂ constant: range to sigma conversion