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The fundamental principles of color-switching at the screen by retarding or accelerating fields with a single electron beam are described. A mathematical analysis is made showing the effects and importance of various voltage and geometric parameters. The focusing effects of the apertures and the uniform fields are fully investigated. A new method of aperture-mask-voltage modulation is given for the accelerating-field case. Single gun tubes using these beam-deflection principles have the advantages of automatic color registry, simple monochrome presentation, short physical length, low color-switching electrode capacitance, and equal numbers of each of the three-color elements. Tubes using the retarding field are advantageous for large size screens, but ones using the accelerating field make much more efficient use of the electron beam. A method of computing aperture positions to give uniform variation in spacings is described. Some of the techniques described in the construction of 16- and 24-inch reflection-type tubes include prevention of microphonics in the screen; printing methods that make webbing lines invisible; glass spacer blocks that withstand high voltage gradients; a method of etching slits in the screen at an angle to reduce beam-current interception; screen alloys that withstand high-power dissipation; and a high-current electron gun.