Example of a U Chart

In this example, you use the U Control Chart launch window to launch Control Chart Builder. You want to create a U chart to monitor the number of defects per subgroup sample size. The data are defect counts in boxes of automobile support braces. A box of braces constitutes one inspection unit. The number of boxes inspected (per day) is the subgroup sample size, which can vary.

1. Select Help > Sample Data Folder and open Quality Control/Braces.jmp.

2. Select Analyze > Quality and Process > Control Chart > U Control Chart.

3. Select # defects and click Y, n Defects.

4. Select Unit size and click n Trials.

5. Click OK.

Figure 3.33 U chart of # Defects 

Because the sample sizes are not equal across subgroups, the limits are uneven. Two of the last five samples are not within the control limits.

Want more information? Have questions? Get answers in the JMP User Community (community.jmp.com).