Based off of that "The Missile Knows Where It Is…" video that popped up in everybody's feed one day and that one siege meme.
"The missile knows where it is at all times. It knows this, because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater); It obtains a difference, or deviation." October 21, 2019