I get the concept of a "true zero" value, but I'm not sure why this implies that there cannot be any negative values—at least that's what most sources say that I found only, with only few exceptions.
But what about a variable like
account_balance? To me, it ticks off all requirements for ratio data, and negative values are meaningful to indicate debt. I can even say that one person has twice as much debt as another person, and a balance of 0 still feels like a "true zero" expressing the absence of any money.
account_balance is not a ratio data, what else should it be then? And why?