New Charts for Variables: Theory and Practice

New Charts for Variables: Theory and Practice (1994)
Zigmund Bluvband, Ph.D., ALD Ltd., Israel
P. Grabov, QA&R, Technion, Haifa, Israe
D.Ingman, QA&R, Technion, Haifa, Israel

The work examines the conventional charting technique for variables and shows that the Shewhart control charts cannot be considered as optimal.
It present an alternative technique based on constructing an elliptical control region on a two-dimensional graph of the measures of process central tendency and spread. The proposed technique implies setting up in single 'pooled' chart on which the plot on the sample standard deviations (or the sample range). The inner couple of limits is used for process stability evaluation, whereas the outer couple serves continuous process quality assessment. The chart allows to reduce the process adjustment errors compared which the conventional charts, and shows the process dynamics from both the stability and capability points of view.