The estimate of process standard deviation, including the effect of measurement error. The best estimate of process variation is from a control chart of the process, as calculated in our SPC software; however, when this data is unavailable, process variation can also be estimated in our gage calibration and SPC software using this formula based on the parts used in the study:
R&R is the variation due to Repeatability and Reproducibility, and
PV is the estimate of actual part-to-part variation, excluding the effect of measurement error.
A better estimate of Total Variation can be obtained through the use of SPC Control Charts. In this case, use the following Total Variation formula:
Ordinate is the specified Sigma Level (commonly 3 (historically 2.575) for Gage R&R analysis)
σprocess is the process sigma, as obtained from an SPC control chart on the process variable.