Since the early days of Wireless, electronic equipment has increased greatly in use and complexity until today it covers a vast field of applications which includes such diverse requirements as: domestic radio and television sets; transmitting equipment; industrial automation; complex computers; air and sea navigational aids and space probes, etc. Though all equipments are expected to give long-term trouble-free service the operational requirements vary widely. These may cover good environmental conditions but with a necessity for a high order of stability; there must be resistance to extremes of temperature and high relative humidity, transportation shocks, aircraft vibrations, atmospheric corrosion or low air densities, etc. To ensure satisfactory performance, equipment must include electronic components which have been tested to prove their fitness for the particular purpose required.