"'''This must be Thursday," said Arthur to himself, sinking low over his beer, "I never could get the hang of… — Douglas Adams

"Come," said Slartibartfast, "you are to meet the mice."

The aircar rocketed them at speeds in excess of R17 through the steel tunnels that lead out onto the appalling surface of the planet which was now in the grip of yet another drear morning twilight. Ghastly grey lights congealed on the land.

R is a velocity measure, defined as a reasonable speed of travel that is consistent with health, mental wellbeing and not being more than say five minutes late. It is therefore clearly an almost infinitely variable figure according to circumstances, since the first two factors vary not only with speed taken 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.

R17 is not a fixed velocity, but it is clearly far too fast.

"Simple. I got very bored and depressed, so I went and plugged myself in to its external computer feed. I talked to the computer at great length and explained my view of the Universe to it," said Marvin.

"And what happened?" pressed Ford.

"It committed suicide," said Marvin and stalked off back to the Heart of Gold.