Optimising the choice of a suitable element is now a process of finding the best compromise (in the opinion of the designer) between the priorities of the system and the availability of the hardware. As far as the factors involving numerical data are concerned, some yield a 'go/no-go' situation which will eliminate those which are too costly, too heavy, too big etc.

Other requirements involving more subjective data should be compared on the basis of their ability to meet the criteria as laid down in the Product Design Specification. This may be an iterative process which converges on the best compromise.