Abstract: Control chart techniques have been widely used in industries to monitor a process in quality improvement. Whenever we deal with variables data, we usually employ a combination of X-bar chart and R chart (or S chart) to monitor both the center and the spread of the process. In this paper, we propose a simple alternative, that is, we design a single chart to monitor both the center and the spread for variables data. When compared with the combination of X-bar chart and S chart, the proposed chart is shown to be just as effective. An example is given to show how to use this new chart.
Key words and phrases: Average run length, control chart, variables data.