
252 A First Course in Quality Engineering
thus calculated� The P-chart then looks like the one shown in Figure 4�11�
These limits are called “stair-step” limits because of the way they look�
Yet another approach is a compromise between the two approaches
described above� In this, the limits for the chart is calculated using an n,
which results in constant limits� If a p
i
value falls close to the limit, then the
limits for that sample are calculated using the exact size of that sample, and
the p
i
value is compared with those limits� This contributes to speedy chart-
ing while also allowing clarication in doubtful cases�
Example 4. ...