For the uninitiated..

Alrite..If u don't know what R 17 is, here goes:

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.

And puh-lease read the book....it is marvellous!