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Total Quality Management - CII Institute of Logistics

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<strong>Total</strong> <strong>Quality</strong> <strong>Management</strong><br />

SPE<br />

C.<br />

.5623<br />

.5622<br />

.5621<br />

.5620<br />

.5619<br />

.5618<br />

.5617<br />

Figure 4.7 Histogram<br />

Let's review each <strong>of</strong> these questions in terms <strong>of</strong> the histogram in Figure 4.7<br />

1. Is the process producing parts to the bell-shaped curve?<br />

Because the histogram is roughly bell-shaped, then for practical applications we<br />

may say:<br />

a. The process appears "normal" and stable<br />

b. Variations are generally due to chance clauses.<br />

However when the histogram is not roughly bell-shaped:<br />

a. The process is not "normal"<br />

b. Assignable causes are influencing the variations. In special cases a frequency<br />

distribution or histogram <strong>of</strong> measurements from a stable process will not match<br />

the formal curve, but in most manufacturing operations, measurements from a<br />

stable process will make a good match to the normal curve.<br />

<strong>CII</strong> <strong>Institute</strong> <strong>of</strong> <strong>Logistics</strong> 76<br />

Website: www.ciilogistics.com

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