Jim Elwell wrote: "But I expect to
buy food by the kilogram long before I drive in kilometers per hour."
But Jim, you already drive in
kilometers per hour, and meters per second, and furlongs per minute, or any
other ratio of distance and time. They're all capable of measuring your
speed.
It's just the speed limit signs that
are in miles per hour, so you conform to the limit (or not),
based on your speedometer's outer scale.
