Tesla T801

Calculator with scientific functions and a vacuum fluorescent display that emits green light. This type of display consists of separate vacuum tubes whose construction is based on a directly heated triode. When viewed from the user, the display contains a filament, a grid and seven anodes covered with phosphor which form the segments of each digit. By connecting a positive voltage to the grid, a certain digit is selected, and a positive voltage connected to an anode will light it up. This kind of displays is still used in audio devices or DVD players.