Constructing an np Chart A variation of the control chart for p is the np chart in which the actual numbers of defects are plotted instead of the proportions of defects.

The np chart will have a centerline value of , and the control limits will have values of 1 3 and 2 3 . The p chart and the np chart differ only in the scale of values used for the vertical axis. Construct the np chart for the example given in this section. Compare the result with the control chart for p given in this section.