The way Six Sigma was presented to me by Mike Harry was that it is a tool for finding out where to apply your effort. I've not been involved in it for a long t

The way Six Sigma was presented to me by Mike Harry was that it is a tool for finding out where to apply your effort. I've not been involved in it for a long time and am sad to hear of his death. The great thing about it as he presented it was that it did not require a great deal of sophisticated tools or a lot of statistical knowledge just a spreadsheet and an appreciation of multi-way analysis of variance. When I was working with engineers using Six Sigma in the late 80s, early 90s, Six Sigma was not really to do with day to day statistical process control. It was all about finding assignable causes of variation and how variability in each part's properties contributed to the variability of the whole. The connection with process control was that it helped you decide what tolerances one could allow. In several cases the Six Sigma investigation resulted in widening the tolerances instead of narrowing them as it was found that they were pointlessly tight and resulting in more costly processes. In many others it resulted in a change to the process, adding steps, replacing parts, etc., and not just an adjustment to the process' parameters.