> I have to do math at every transaction? There's different denominations (which make no sense), and some are paper and some are metal? How do I authenticate th

> I have to do math at every transaction? There's different denominations (which make no sense), and some are paper and some are metal? How do I authenticate that it's a real bill? What happens when it wears out? Are you really going to keep inventing new designs every couple years as criminals learn to make their own? What if I want to buy something and I have enough cash but the vendor can't "make change" (actually happened to me the other day)? In practice, these won't be significant problems for the user. I haven't seen the focus group testing, but I'm comfortable predicting that. Some of those issues are problems for the cash-issuer, not the user.