Daniel's friend in England measures distance in miles but temperature in Celsius and weight in kilograms.

That inconsistency turns out to tell a much bigger story.

The metric system was created during the French Revolution to replace a chaotic patchwork of local measurement standards across Europe. Different units with the same name could mean different things in different places. Revolutionary France designed something entirely new -- a universal decimal system originally tied to the size of the Earth itself. Today the meter is defined using the speed of light, but the original ambition was to base measurement on nature rather than tradition.

Metric eventually became the dominant system around the world. The United States has been a prominent exception -- but the story is more complicated than most people realize.

The US  ...