Misstating what analog means   While the explanation given direct correspondance to a physical property may have originally have been true I will not presume to judge this it is not in accordance with modern usage The difference between analog and digital can with some oversimplification be stated as the difference between a continous dependency and one that considers eg a signal a series of discrete information units This statement is off the top of my head and may be suboptimally formulated the principle is still correct A physical dependency is only needed in as far as everything including the digital signals in a computer ultimately has some physical connection