I just thought of a rather bizarre idea.
A unit of currency in which there is only one unit in existence, and everybody has fractions of that unit. For example, positing a gross world product of $4*10^12, one dollar would be &2.5*10^-13 SUC (Single Unit Currency).
This could be shortened or made more understandable in some way, say &2.5e-13 SUC, or some similar notation. Or, perhaps having a word for e-13 would be good.
This would be interesting, because all the money in the world would be 1 SUC. If someone every had anything even closely approaching this number, that would mean something was seriously distorted and wrong about the economy.
I'm not sure how the whole creation of money through lending money that's also stated to be on deposit that banks do would work with this system. But, I think it's an interesting puzzle to contemplate.