Use C Chart to monitor the number of defects where each item can have multiple defects. You should use a C chart only when your subgroups are the same size. Use this control chart to monitor process stability over time so that you can identify and correct instabilities in a process.
For example, an LCD manufacturer wants to monitor defects on 17-inch LCD screens. Technicians record the number of dead pixels for each subgroup of 10 screens per hour and use a C chart to monitor the number of dead pixels.
The chart shows that, on average, technicians find 10 dead pixels in each sample. Sample 17 is out of control. The technicians should identify any special causes that contribute to the unusually high number of dead pixels.
To create a C chart, choose .