Here’s a trivia question for you: How many countries today measure temperature in Fahrenheit?

We’ll get to the answer through a story.

By the 1600s, scientists had invented early thermometers. Using air, then alcohol, then mercury—all things that expand with rising temperature—they could tell you … if it was hotter or colder.

But they couldn’t tell you by how much, because no one had standardized a way to measure it.

Around 1700, German scientist Daniel Fahrenheit came up with a scale. He found the coldest temperature he could achieve in his lab using a mixture of ice, water and salt and called that zero. Then used the approximate temperature of the human body as 100.

This made the freezing and boiling points of water at sea level the rather random numbers of 32 and 212. But he put his scale on his new glass thermometer. And because it was the most accurate instrument to date, it stuck.

In the 1770s, British scientists adopted it, then standardized it across the entire British Empire.

Meanwhile, the rest of Europe adopted a simpler scale devised by Swedish astronomer Anders Celsius. Also called centigrade, it used the freezing point of water as zero and boiling as 100.

In the 1960s, the Brits, too, switched to Celsius, leaving the U.S. and just five former British colonies—all of them small island nations—stuck on Fahrenheit.