(And of course currencies have been digital, as opposed to analog, for thousands of years, and one of the leading hypotheses on the origin of digits as a way of representing numbers is that they were used for accounting. "Digital" is not simply a synonym for "electronic"; rather, it's the practice of representing numbers or other information as sequences of discrete, arbitrary symbols, rather than continuously varying quantities of something like weight, width, or voltage; symbols such as "4", coins, or cuneiform glyphs.)