The UCL and LCL for an x chart are 25 and 15 respectively. The central line is 20, and the process variability is considered to be in statistical control. The results of the next six sample means are 18, 23, 17, 21, 24, and 16. What should you do?
Required for credit: draw a chart carefully labeling all parts: UCL, LCL the mean and all sample points, to support your answer: