U chart Example

The Braces.jmp data in the Quality Control sample data folder records the defect count in boxes of automobile support braces. A box of braces is one inspection unit. The number of boxes inspected (per day) is the subgroup sample size, which can vary. The U chart in Figure 3.27 is monitoring the number of brace defects per subgroup sample size. The upper and lower bounds vary according to the number of units inspected.

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

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

3. Select # defects and click Y.

4. Select Unit size and click n Trials.

5. Click OK.

Figure 3.27 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).