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 AdamsDirk turned on the car wipers, which grumbled because they didn't have quite enough rain to wipe away, so he turned them off again. Rain quickly speckled the windscreen. He turned on the wipers again, but they still refused to feel that the exercise was worthwhile, and scraped and squeaked in protest.
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