The development and design of precision engineering equipment and components call for a great deal of versatility on the part of the designer. Unlike conventional parts and machines, which can be made direct from drawings, precision engineering is often a matter of trial and error, for it often happens that the designer cannot be sure beforehand whether the equipment will conform to the given specification. Apart from having to choose from an extraordinarily wide range of materials, he has to take into account a great many incidental, but nevertheless important, factors such as: safety requirements, styling, planning, production facilities and so on. This makes his task quite difficult, so rarely is the design entirely satisfactory straight away. Only after tests have been carried out, and models constructed, will he be able to judge whether the design comes up to expectations.