As all physicists know, all units are arbitrary. The numbering system is anthropocentric; for example, the Celsius scale of temperature has 100 degrees between the boiling point of water at STP and the freezing point of water. The number 100 is chosen because human beings have 10 fingers. The best units might be based on physical constants, for example, defining temperature in terms of absolute zero and the triple point of water, which are presumably the same everywhere in the universe. Even these units are anthropocentric, though, because, for example, why should water be more fundamental than another material? (Answer: only because we live on Earth, where the abundance of liquid water has made our lives possible.) The basic SI units (base units, see Sec. 2) are as arbitrary as any other set. [For Part I, see EJ945887.]