Publication date: 08/13/2020

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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