the process status, or not correctly detect changes. A problem with this is that due to the high prob- ability of false alarms, the true signals may be ignored. Another problem arises in the vicinity of zero defects or nonconformities. When the process works with high quality, that is, when many samples lack nonconformities, it often happens that the lower control limit is less than zero, which makes the interpretation of the process behavior very difficult. Improvements cannot be easily detected and reading the runs is hard to understand. The control upper limit can be less than one unless the sample size is large. In these cases, any sample containing only a nonconforming item will cause a false alarm signal, invalidating the control itself.