My first reaction to being asked to speak on this subject was that it is the user and not the producer of model data whose views we want to hear, and I am glad to say that Mr. Ellis has agreed to co-ordinate with me, so that I have some inside knowledge to draw on, if I venture to say what a designer does.

I wish in the main, however, to take the title in rather a different way, and to discuss in what sense model tests can be expected to give results useful to the designer.