The nature of the instability of an unregulated free-enterprise system is only now beginning to be clearly understood. Perhaps the degree of understa… - Arnold Tustin

The writer, who as an engineer has spent most of his life in factories, is inclined to look at the basis for investment from a technological point of view... Consider … the class of industrial investments only... The situation is one of entrepreneurs and boards of directors considering, from time to time, various ’possibilities of investment’, such as extra lathes or looms, an extension to a factory, a venture in some completely new product, and so on. It is helpful to think of these ’opportunities for investment’ as existing, in a given situation, in great number and variety, whether they are at that moment under active consideration or not. When any such possibility is considered it is assessed in respect of ’expected profitability’. One may conveniently think of all possibilities of investment as ’quanta’ that can be placed in a schedule of small ranges of expected profitability according to these assessments. The placement of a given ’opportunity for investment’ on this schedule has some ’margin of uncertainty’ (a curious analogy with the case of the quanta of physics).

It is possible that the major collaboration between economists and engineers is still to come, in the greater use of physical analogues and computers of the analogue type to avoid the difficulties of calculation. Apart from their major use as possible tools for economic regulation, physical analogues have a subsidiary use, for there are students of economics, as there are many students of engineering, who can better understand the significance of the somewhat formidable mathematics that tends to be used in this field, if they can first acquaint themselves with the types of behaviour in question as exhibited by physical objects that can be seen, felt, handled and experimented with. It may also be suggested that economists may find that what they have to say about economic policy will be very readily assimilated by one group of attentive pupils, namely the scientists, engineers and technicians of industry, if explanatory notions can be drawn from the theory of automatic control, which is now part of a normal engineering education. The aim of this essay has been to give explanations of system behaviour, and some approaches to its analysis, using geometrical construction and physical analogy where possible to clarify the implications of the more usual formal algebraic approach.

The striking parallel between the economic models that are currently under discussion and some engineering systems suggests the hope that in some way the rapid progress in the development of the theory and practice of automatic control in the world of engineering may contribute to the solution of the economic problems.