• R is a velocity of measure, defined as a reasonable speed of travel that is consistent with health, mental well-being, and not being more than, say, five minutes late. It is therefore clearly as almost infinite variable figure according to circumstances, since the first two factors vary not only with speed as an absolute, but also with awareness of the third factor. Unless handled with tranquility, this equation can result in considerable stress, ulcers, and even death.

    Douglas Adams (2012). “The Hitchhiker's Guide to the Galaxy Radio Scripts Volume 2: The Tertiary, Quandary and Quintessential Phases”, p.111, Pan Macmillan