Methods and systems of determining a failure copula for a consumable are disclosed. The invention also relates to a surge arrester arrangement, to a use of an electrical insulator for insulating a surge arrester, and to a method for production of such an electrical insulator. 35, can be used as a brightness enhancement film, and further that provides an excellent visibility satisfactory also when observed not only from a front direction but from an oblique direction in image viewing displays, such as liquid crystal displays. Monitoring of upstream performance for overperforming or underperforming modems can be carried out, and new upstreams with higher andor lower throughtput can be created to service the overperformers andor underperformers. Such vessel can perform installation functions of sub-surface assets such as tidal turbines, wave energy devices, cable laying and the like, or to facilitate foundation installations and also the function of inspecting sub-surface areas.