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 has a centerline value of np, and the control limits have values of np̅ + 3 √np̅q̅ and np̅ - 3√np̅q̅. The p chart and the np chart differ only in the scale of values used for the vertical axis. Construct the np chart for Example 1 "Defective Aircraft Altimeters" in this section. Compare the np chart to the control chart for p given in this section.