For lots of measures you're correct, but that's not really true for all cases. Even in highly-metric France they use but cuiellères a soupe and so forth in addi

For lots of measures you're correct, but that's not really true for all cases. Even in highly-metric France they use but cuiellères a soupe and so forth in addition to mL, because it's a more convenient measure. An egg matches with about a cup of flour for a batter--eggs don't exist in fractional powers of ten. I also think (again in common household uses like setting a thermostat or talking about the weather or a fever) a fractional degree celsius is false precision, since you can't feel it, and a whole degree celsius is too coarse, so something that ranges from 0-100 in the temperatures you're likely to encounter is better than a scale which ranges from 0-100 over (the equally arbitrary) liquid phase of water. Of course it's marginal, but it's not entirely true that (unlike the metric system) all these measures are totally arbitrary. There are advantages and disadvantages to these systems. If you have to convert inches to miles a lot--yeah, the metric system performs much better for that. But conversions of scale or dimension--while extremely common in science and engineering--are not likely in common usage, while fractional division is much more common. It's likely that you don't recognize the advantages of an alternate system merely because you're unfamiliar with it.