Electrostatic deflection from a common center is possible by the use of electrostatic yokes, or Deflectrons. These consist of a 4-terminal pattern, printed on the inside of glass cylinders or cones. An analysis of the pattern geometry is presented which gives simple expressions for deflection factor of electrostatic yokes. The theory also accounts for a small residual noncircularity of scan, and gives clues as to its correction. Equipment to test tube performance is described, including ultraviolet mapping and electronic detection of the axis. The most suitable type of post-accelerator for use with Deflectrons employs a long drift space, bounded by a metallic mask, and confines the high gradient to a narrow region close to the screen. It is shown that this mask intensifier suffers from secondary emission. This effect can be effectively suppressed by an insulating coating of the first surface of the mask, while connecting the support metal to a lower potential than the drift space. The resulting double layer of charges prevents the escape of secondaries towards the screen. This barrier-mask intensifier permits post-acceleration ratios of 10 to 1 without loss of deflection.