The commercial success of an engineering design (whether of a large-scale plant or individual product) depends largely on the technical, economic and aesthetic merits of the design, and although these merits can to some extent be judged independently, the design process itself involves a close study of the complex and dynamic interrelationship between them. Even a superficial examination exposes this interrelationship between the technical, economic and aesthetic aspects of design. For example, a technically efficient design often leads to profitable manufacture and the lack of aesthetic merit can cause commercial failure, particularly in the case of consumer goods. Conversely, the desire for high technical merit in a design can raise subsequent production costs to a point where financial success is endangered. The successful design is therefore a compromise involving an optimum combination of technical, economic and aesthetic merit. This optimum combination can be arrived at qualitatively or quantitatively by the individual designer or by a large team of engineers, "designers' and economists. It is undoubtedly successful optimization that has led to the design of such a plant as the Scottish Agricultural Industries fertilizer factory at Leith, or such a product as the "Mini" motor car, or such buildings as those designed and constructed by Nervi in Italy. Quite clearly there are other factors, such as social and political needs, which can affect the design and manufacture of a plant or product; but in most industrial environments techno-economic design considerations are often paramount, with the aesthetic aspects influencing in a less quantifiable way the eventual design. The "information flow diagram", shown in Figure 18.1, indicates the interaction between these three aspects and their place in the overall design and production scheme.