Ok so this week I was studying aerodynamic differences between a "Fat Man" bomb which was dropped on Nagasaki and the Aim 120c Air to Air Missile. What intrigued me with nuclear weapons was the "Variable Yield", SO I did some research to see how it works . I couldn't mind much on how to adjust a nuclear weapon - Not surprising. Im just curious whether its adjusted by adding or removing fissionable material or is there some shielding mechanism to prevent all of the material undergoing fission. My second idea seems more safe and logical to me, I was thinking of a mechanism similar to that of a Artillery fuse in mortar shells which are adjusted with a special tool. Then again fuse has nothing to do with the size of the explosion in a shell.