But if stupid Americans can use the "difficult" system, it can't be too hard.
I think about this whenever I see someone complain about how Fahrenheit is arbitrary and how are you supposed to remember that water freezes at 32° and boils at 212°. I guess American brains are just able to retain more.
If I were launching an air raid on a flat earth, I'd have the planes fly over the edge and under the earth. They wouldn't be able to see you coming.