16Verification and Validation

I often say that when you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be.

(William Thomson, Lord Kelvin, 1891)

Managers need to measure the performance of their operations for two important reasons: to evaluate the performance relative to goals and to control the processes. But Lord Kelvin goes further, suggesting that without measurement, you simply do not know what you are talking about. Although referring to science, Lord Kelvin’s comments are appropriate to industrial processes. Periodic measurement of industrial processes is necessary because they are dynamic and subject to change. In Chapter 13, Shewhart tells us that process variability is inevitable. In Chapter 11, Chesterton warns that a ...

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