Since manufacturers change their component suppliers, or other details of the specification, from time to time, to be absolutely sure of millennium compliance it may be necessary to test each unit of a specific model individually. Set out below are some examples of types of technology which experts have already identified as Y2K vulnerable, together with some illustrations of impact. Most electricity generating stations, whatever fuel they use and including hydro-electric, will have more than one millennium vulnerable unit. There are many other applications which use this sort of moving average as a safety check, eg engine controls, flight controls, life support kit. Whether all nuclear power stations would failsafe is not clear.
Automated systems are probably millennium vulnerable and by no means certain to failsafe.
Millennium testing is crucial. Some types of valve are known typically to fail shut, others to fail open. Accidental oil contamination cannot be ruled out. Telecommunications National telephone networks are heavily reliant on micro-chips and just as vulnerable to progressive collapse as power grids . Cellphones typically contain microchips which, in older systems in particular, may be millennium vulnerable, together with the exchanges.