Publication date: 07/30/2020
Control Limits for P and NP Charts
The lower and upper control limits, LCL, and UCL, respectively, are computed as:
P chart LCL = 
P chart UCL = 
NP chart LCL = 
NP chart UCL = 
where:
is the average proportion of nonconforming items taken across subgroups
ni is the number of items in the ith subgroup
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