First you have to make it yourself, then you can buy a kit. In both of these steps we have the stage of "Will it work?". A knowledge of how it works is essential and intervention is needed at all times.
Then, you can buy it in one or two models only at a specialty store, later at a department store. We are now in the "Which one will work best?" stage. Knowledge of how it works is not vital to the experience, but you can make it better if you know.
Finally, since more than three steps needs a book to support it, we come to the stage where you can buy it at 7-11 or the corner drug store in knockoff form, as well as a variety of models in department and discount stores. Knowledge of the inner workings is impossible without a degee, or a degree of obsessive/compulsive disorder and monomania, and is discouraged by the manufacturer. This is the "How fast will it go, Mom?" stage.
I'd say we are approaching the middle of Step Two.
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