U Chart: You can expect between 0.04 and 1.927 dead pixels are expected on each screen. Because of the unequal subgroup sizes, the control limits will vary.
Plots the number of nonconformities or defects per unit. It is possible for a unit to have one or more nonconformities but still be acceptable in function and performance.
For example, the number of nonconformities per 50 running feet of carpet, or the number of dead pixels per foot of LCD screen. You can look at one type of defect such as dead pixels, or you may look at several nonconformities together such as dead pixels, stuck pixels, scratches, and blurry spots. LCD screens may have 2 or 3 dead pixels, yet still be an acceptable monitor.
The following U chart plots the number of dead pixels found on each unit (screen).
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U Chart: You can expect between 0.04 and 1.927 dead pixels are expected on each screen. Because of the unequal subgroup sizes, the control limits will vary. |
Another chart that plots defects is the C chart. However, the C chart plots the number of nonconformities per sample and is useful when the subgroup size is constant.