Example of a UWMA Chart
In this example, a legacy UWMA control chart with a moving average span of three is examined. The measure of interest is the gap between the ends of manufactured metal clips. To monitor the process for a change in the average gap, subgroup samples of five clips are selected daily.
1. Select Help > Sample Data Folder and open Quality Control/Clips1.jmp.
2. Select Analyze > Quality and Process > Legacy Control Charts > UWMA.
3. Select Gap and click Process.
4. Select Sample and click Sample Label.
5. Change the Moving Average Span to 3.
6. Click OK.
Figure 14.21 UWMA Charts for the Clips1 data
The point for the first day is the mean of the five subgroup sample values for that day. The plotted point for the second day is the average of subgroup sample means for the first and second days. The points for the remaining days are the average of subsample means for each day and the two previous days.
The average clip gap appears to be decreasing, but no sample point falls outside the 3σ limits.