Apparatus for use in audio-visual communication; racks and mountings specifically adapted for use with audio, visual, computer and telecommunications equipment; digital video adaptors for use with computers; audio cable; audio cable connectors; apparatus for linking computers into networks; cable for electrical transmission; cabling networks (installations) incorporating fibre optic cables; communications cables; computer cables; data transmission cables; fibre optic cables; telecommunications cable; data security instruments; computer networking apparatus; computer software for time control; data logging apparatus; data switching apparatus; data transfer apparatus; data transmission cables; wire free data transmission apparatus; uninterruptible power supply apparatus (battery); apparatus for use in audio-visual communication; electric leads; cables for signal transmission systems; cases adapted for television display apparatus