Independent researchers and practitioners have conclusively shown that inspectors make mistakes, classifying bad items as good and vice versa. This paper mathematically and graphically examines the effects of inspection error on the p chart. The point of view that control limits are based upon a target value, and the point of view that control limits are based upon error prone data, are both considered. Further, a compensating p chart is offered to help provide an OC curve closer to that desired. Also, the OC curve of a p chart under variable error rates is explained and illustrated.