Temperatures have plummeted in Connecticut, with wind chills dropping to nearly 20 degrees below zero. But how is that number actually calculated? To learn more, I called up the scientist responsible for developing the latest iteration of the wind chill chart, who told me about the colorful — and changing — history of a number you hear a lot about in New England.

On it’s most basic level, wind chill represents “represents the effect that the wind has on the rate at which you lose heat from the body,” said Maurice Bluestein, a professor emeritus of mechanical engineering and one of the scientists responsible for the latest iteration of the wind chill chart.

But objectively quantifying what’s essentially a feeling has always been difficult, which means the way wind chill got calculated over the years has changed a lot.

To understand that part of the story, Bluestein said, we need to go back to the 1940s. There was an Antarctic expedition led by some geographers who wanted to develop a chart that would quickly let soldiers fighting in the cold European theater of World War II know how temperature and wind speed could contribute to frostbite.