### Estimates of Standard Deviation Based on Control Charts

The following calculations of estimated standard deviation are used in the calculation of capability indices for control charts:

Sigma Based on the Range:

where is the average subgroup range from the XBar & R or X Tilde & R Chart and is the standard SPC constant based on the subgroup size.

Sigma Based on the Subgroup Standard Deviation:

where is the average subgroup standard deviation from the XBar & S Chart and is the standard SPC constant based on the subgroup size.

Sigma Based on the Paired Range:

where is the average subgroup range from the RX Chart and is the standard SPC constant using subgroup size 2.

Sigma Based on the Moving Range:

where is the average subgroup range from the XMR(2) Chart and is the standard SPC constant using subgroup size 2.

where is the average subgroup range from the XMR(3) Chart and is the standard SPC constant using subgroup size 3.

See also:

Capability Indexes: Table of Calculations