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Now let us turn to cathode-ray tubes (abbreviated CRT) that provide a visual representation of voltage and current waveforms. Cathode-ray tubes consist of three basic components: 1. the electron gun, 2. a deflection system, 3. a fluorescent screen. These essential parts of a cathode-ray tube are mounted inside a highly evacuated, funnel-shaped glass envelope the large end of which has the fluorescent screen coated upon the inside surface.