system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is a physical standard still needed for the kilogram?

I understand that it allowed everyone back in the day to figure out how much mass something had and generally find agreeing numbers. However,  do we not know the masses of enough things in kilograms where you could just cross-check to determine mass rather than have a standard?

Also, have we figured out why the standard kilogram has been losing mass?
gpt
we can't cross check. it doesn't work that way. we need to have one standard, or one equation describing what kilogram is. we need to find a way, maybe by ideal sphere of atoms and then counting them, or by something different.

and AFAIK it's not losing mass.