Total Variation for Gage R&R Study

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:

where:

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:

where:

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.

Learn more about the Quality Improvement principles and tools for process excellence in Six Sigma Demystified (2011, McGraw-Hill) by Paul Keller, or his online Green Belt certification course ($499).