There is provided a mobile radio communications network device operative to collect network performance measurements and to select at least one mobile radio communications device from which network performance measurements are to be collected if at least one parameter of the at least one mobile radio communication device corresponds to at least one specified selection parameter. The first and second diffusion layers of each dummy cell are commonly connected by use of a wiring. A distal portion has an outer surface and an inner surface partially defining a passage. The edge hem having a free edge that folds inwardly over the inner face of the screen and is parallel to, and spaced above, the inner face of the screen.