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 12.25 is monitoring the number of brace defects per subgroup sample size. The upper and lower bounds vary according to the number of units inspected.
Note: When you generate a U chart, and select Capability, JMP launches the Poisson Fit in Distribution and gives a Poisson-specific capability analysis. To use the Capability feature, the unit sizes must be equal.
1. Select Help > Sample Data Library and open Quality Control/Braces.jmp.
2. Select Analyze > Quality and Process > Legacy Control Charts > U.
3. Select # defects and click Process.
4. Select Date and click Sample Label.
5. Select Unit size and click Unit Size.
6. Click OK.
Figure 12.25 U ChartÂ
