Variation is the bane of quality, yet variation is as much a part of everyday operations as the sun is of daylight. In process analysis, statistics provide essential clues as to the causes of variation in a process.Variation is normal and largely unavoidable in many cases. Consider the simple act of walking across a room while carrying an overfilled cup of coffee. No matter how careful we might be the very act of walking introduces a certain amount of random jiggling and some of the coffee may spill. This random movement constantly changes the relative surface of the liquid relative to the floor, and, at the same time, there is an element of up and down movement that complicates the task. Other factors, such as the smoothness of the floor or a momentary twinge in the knee, can add still other, often-unknown, movements. The point is that all of these factors are in play at the same time and are common to the act of walking.
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