Related: your business logic should work on metric units. It is a UI concern if the user wants to see some other measurement system. Convert to feet, chains, cubits... or whatever obscure measurement system the user wants at display time. (if you do get an embedded device that reports non-metric units convert when it comes in - you will get a different device in the future that reports different units anyway)

You still have to worry about someone using kg when you use g, but you avoid a large class of problems and make your logic easier.