The core of most monitors is the cathode ray tube (CRT), the same as in your TV. But a monitor displays an image of much higher resolution. An image is made up of pixels - much like a newspaper picture is made up of dots, except that pixels on a computer monitor are much tinier and closer together. An average monitor can display hundreds of thousands of pixels; the more pixels, the better the resolution.

You can choose between traditional CRTs, flat monitors and thin film transfer (TFT) screens mounted in picture frame-like stands. A flat display reflects less ambient light than the traditionally convex CRT, and therefore reduces glare and eyestrain. TFT displays are less than two inches thick - very space efficient. But they are more expensive than traditional monitors.

IBM-compatible and Macintosh computers require different types of monitors. After you decide on a platform, there are three things to consider when choosing a monitor: color, size and resolution.

• Color. The quality of a color monitor is judged not only by number of pixels, but by numbers of colors. Better monitors display from 256 colors to millions of colors. The more colors that are available, the more realistic the overall picture is.
• Size. Like TV screens, computer monitors are measured diagonally. The most common size is 14 inches. If you use your computer for graphics, large spreadsheets, or desktop publishing, your screen should be large enough to display a full page of text or graphics (17 to 25 inches).
• Resolution. Pixel resolution of a monitor screen is measured horizontal by vertical. On a low-resolution screen, lines and character edges may appear jagged. The most common resolutions for IBM-compatible PCs are 640 horizontal x 480 vertical pixels (VGA, video graphics array) or 800 x 600 (super VGA).

A 1024 x 768 high-resolution monitor displays clear, sharp-edged characters and graphics, for images with a high degree of detail.

Individual monitors also differ based on dot pitch, essentially the size of the individual pixels. The lower the dot pitch, measured as fractional millimeters (.25mm, .28mm, etc.), the better.

Accessories

Watching computer monitors can result in eyestrain after long periods. Two accessories minimize this eyestrain.

• Anti-glare filters or screens. Made from mesh or optically coated glass, these cut down on reflected light. Mesh screens are less expensive than glass, but harder to keep clean.
• Tilt platform. A stand that rotates, tilts and swivels the monitor to a comfortable viewing angle.

Platform arms attach to the wall or desktop and keep your monitor off the desktop surface and moved aside when not in use. Be sure these arms can bear the weight of your monitor.

If you own a larger monitor, ask about the weight load of a monitor arm platform before you buy.

Maintenance

A computer monitor is susceptible to dirt and dust build-up and should be cleaned regularly. But computers generate static, and household window cleaners create a film that will attract even more dust.

Instead, use sprays or commercially prepared, solution-saturated pads. Do not spray cleaner directly onto the screen: the liquid can seep behind the cabinet and get into the circuitry. Spray on a lint-free cloth, then use the cloth to clean the screen.

Always turn off the monitor before cleaning.

In older monitors, an image that stays on a screen too long can burn a permanent image into a screen's phosphors. After a while the image remains visible as a faint outline, even when the monitor is turned off. There is no way to repair this damage.

To prevent "screen burn," you can turn down the screen's contrast, put the PC to "sleep" (a low-power status), turn off the monitor altogether whenever you will be away or install a screen saver.

After any brief period of computer inactivity, screen saver software replaces the static image on the screen with constantly shifting images. Many screen savers offer swirling impressionistic art, images of movie characters or scenic shots.

Modern monitors are built to constantly "refresh" the screen from moment to moment, eliminating the need for a screen saver.