Example of C chart with customized control limits
main topic
     interpreting results     session command     see also 

Suppose you work for a linen manufacturer. Each 100 square yards of fabric can contain a certain number of blemishes before it is rejected. For quality purposes, you want to track the number of blemishes per 100 square yards over a period of several days, to see if your process is behaving predictably. You want the control chart to show control limits at 1, 2, and 3 standard deviations above and below the center line.

1    Open the worksheet EXH_QC.MTW.

2    Choose Stat > Control Charts > Attributes Charts > C.

3    In Variables, enter Blemish.

4    Click C Chart Options, then click the Limits tab.

5    Under Display additional sigma limits at, enter 1 2 in These multiples of the standard deviation.

6    Under Place bounds on control limits, check Lower standard deviation limit bound and enter 0.

7    Click OK in each dialog box.

Graph window output  

 

Interpreting the results

Because the points fall in a random pattern, within the bounds of the 3s control limits, you conclude the process is behaving predictably and is in control.

Minitab help Stat Graph SixSigma DOE Glossary Reliability SPC,MSA,CPK
Create Pareto chart