easiest way to probably help would be to use the difference between inches and feet.
(assuming they understand that (and that they understand the us customary system))
You mustn’t speak those words here. Those are the forbidden tongue. Even greater Heresy to imply there is any practical application of the forbidden knowledge. It upsets the emperials.
But don't be alarmed, all right? Although if you do feel alarmed, try to hold onto that feeling, because that is the proper reaction to being told that you've got brain damage
(assuming they understand that (and that they understand the us customary system))