R17 (Hitchhiker's Guide to the Galaxy)

R is a fictional measure of velocity in the "Hitchhiker's Guide to the Galaxy" series by Douglas Adams. Its description is given as follows:

"R is a velocity measure, defined as a reasonable speed of travel that is consistent with physical health, mental wellbeing and not being more than about 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 tranquillity this equation can result in considerable stress, ulcers and even death.

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