The results of the regression analysis of V to d, [R.sub.c], [E.sub.s], and Et, respectively, are shown in Figures 4, 5, and 6 in terms of
scatter diagram and regression line, while Table 5 reports the regression equations and the related coefficient of determination [r.sup.2].
Sigma uses the base tools to improve the quality of products and processes as MSA (Measurement System Analysis), IPO Diagram (Input-process-output), CE (Cause-and-effect diagram), Histogram, Pareto diagram, DMAIC (Define, Measure, Analyze, Improve, Control) , Run chart, Control chart,
Scatter diagram, Regression Analysis, DOE (Desing of Experiments), FMEA (Failure Mode and effect analysis), SOP (Standard Operating Procedure), QFD (Quality Function Deployment.