Abstract
In summary, a range of criteria have been developed by many experimenters, the work of a few being mentioned here as examples of different approaches. Criteria and associated measurements range from the crude and rigid at the start to the sophisticated and flexible at the end, and at each step along the path from the beginning the number of assumptions decreases and the complexity increased. There is a limit, set by the uncertainty of the meteorological data at one end of the scale to the variability of people's reaction to wind at the other, beyond which it is uneconomic to proceed. It is suggested that this limit has now been reached and in the future only refinements will take place.