Been doing this for years. I evangelize it all the time, and people still don't understand, or they try to make it more complicated than it is. But it's literally THIS easy, so easy. It's not even math at this point, especially if you only double the dollar amount and ignore the change, a kindergartener could do it.

Yet people refuse to learn a "new weird way".

You don't have to understand it, just do it. This is literally the easiest way. I will die on this hill.