More on Computer Monitors
Dear  [Lynn],
[Adding more information about monitors. See the  previous post  for more details.]
Ah yes. Now that you mention this, I know what it is. The aperture grill is a thin metal screen, situated inside the monitor viewing tube, just behind the viewing surface of the picture tube (a.k.a Cathode Ray Tube or CRT for short). Its purpose is to attract and help aim the electron beams from the electron guns at the back of the CRT, so that they strike the intended phosphor pixels, and produce the correct color of light at the right location on the screen. These openings also regulate the SIZE of the electron beam, much as you can control the size of a spot of sunlight if you poke a hole in an otherwise opaque card and allow the sunlight to pass through and strike the ground or a desk top. the bigger the hole you poke, the bigger the resulting spot of light. The bigger the AG pitch, the less precisely the electron beams can be aimed. Even if you have very small dot pitch (size of the phosphor pixels), a large AG pitch means that even though the beam is being aimed at one pixel, it may be too large to strike just ONE pixel. The resulting spot of light is bigger than one pixel, and the bigger it gets, the more pixels it encompasses. Lower resolution results from a big AG pitch, just as it does from pixel dot pitch. So, the smaller the AG pitch, the better the monitor, and the more expensive it is, of course.
Tom