Variation is a serious thing

Many parts have to fit together to make a product, like a cell phone. When engineers design the parts, they account for the fact that all parts will display some amount of variation as they are produced. Variation is the degree to which a part, product, service, or transaction differs from all others in the same class or category.

In the case of a phone, each class of parts, like the plastic casting, vary in size, weight, and even color. Just as the phone cases vary, so does the clear plastic display that covers the liquid crystal display. Then you have the many hinges, buttons, antenna, internal component, and so on. All these parts have to snap and fit together well if the phone is to perform its function to your satisfaction. In other words, you can only tolerate a certain amount of variation. A little too much variation and the phone won’t work property. A little more variation and it won’t work at all.

And we all know who’s going to end up with the bad phone, right?