The only real display issue with the aperture grille is that it is held in place by thin wires running horizontally behind the display, which are often visible to the user. Aperture grilles can also loosen over time, causing some distortion. The newer NEC and Panasonic displays offer neither a shadow mask nor an aperture grille, but a kind of hybrid called a slot mask . The slot mask consists of oval-shaped holes that allow more of the electron beams to reach the phosphors, thereby resulting in a brighter display. The only real distortion potential stems from the oval shapes, but since electron beams grow increasingly oval as they near the sides and corners of the display, the shapes don't produce new forms of fuzziness but only exacerbate existing distortion possibilities.
Trapezoid distortion alters the rectangularity of the display.
The electronic controls that are part of the monitor determine how the beams from the electron guns move through the deflection system and strike the phosphors, adjusting for the constantly differing angles and paths taken by the beams on their way to the display face. Often, however, the controls can lose their adjustment, resulting in a distorted overall shape of the display. Barrel distortion causes the top and side edges to appear rounded outward, instead of straight up and down for the side edges and straight across for the top and bottom edges. The opposite of barrel distortion is pincushion distortion , where the top, bottom, and sides appear to round inward. Most monitors offer controls to adjust these distortion types as well as trapezoid distortion , where the top and bottom edges are straight across and parallel to one another, but the side edges are straight but not parallel.