It's a math calculation and estimation, not a real measurement. There is not a single place in the USA where it reached -75 today on any device. Weather forecasters just like to use extreme language to make people in their living rooms feel like they are surviving insane conditions.

There is a move among some weather authorities to eliminate references to wind chill and instead focus on the amount of time it takes to freeze skin, which is the real concern here.

I am in Detroit. It is -9 as I write this, but the weather people will try to make that sound like -45 or -50. But it isn't anything like that unless you stand naked in the snow and wind. And then after 10 or 15 minutes it's moot.