"It is just an arbitrary scaling factor!" Uncle Red says witheringly. "This is why I ended up agreeing with your brother Tom, though I didn’t at first, that we should take a cue from the way he and the other relativistic physicists do it, and just arbitrarily set [tau] = 1. Which forces us to deal with fractional values, which I thought some of the ladies, present company excluded of course, might find confusing, but at least it emphasizes the arbitrary nature of the scaling factor and helps to eliminate that source of confusion." Uncle Tom tracks asteroids in Pasadena for the Jet Propulsion Laboratory.