 due to local charge accumulation), instead of bouncing through the hole to strike a random (wrong) spot on the screen.Another type of color CRT uses an aperture grille of tensioned vertical wires to achieve the same result.Due to limitations in the dimensional precision with which CRTs can be manufactured economically, it has not been practically possible to build color CRTs in which three electron beams could be aligned to hit phosphors of respective color in acceptable coordination, solely on the basis of the geometric configuration of the electron gun axes and gun aperture positions, shadow mask apertures, etc.