How'd you like to increase your office productivity by as much as 50 percent? Add a second monitor to your computer setup. You'll never go back to using only one monitor again.

You can open a document or presentation on one monitor and use the other to do research on the Web. Or see your e-mail arrive as you work. Photo and video editors can have an image open on one monitor and the tool bars on the second.

WHAT YOU NEED

Adding a second monitor is easy. First, check that your computer has a dual-output video card. If it has a single-output card, you'll need to add a second video card.

A dual-output video card runs about $100. A single-output card costs slightly less. Many newer computers already support dual monitors, though.

Installing a video card isn't difficult, but an electronics store also can install it for a fee.

You could buy an external monitor adapter, but internal cards perform better. If you use two cards, they should have the same specifications so there's no lag between the monitors.

CHOOSING A MONITOR

The experience is better if the monitors are identical or at least the same size. Go for a 19-inch monitor if possible, or a 17-inch screen. Anything larger than 19 inches may strain your eyes if you sit close.

The monitors and computer should have matching ports. Many monitors have both VGA (analog) and DVI (digital) connections. This makes it easier.

Before buying a monitor, judge the picture quality in the store. The contrast ratio is the difference between the whitest whites and the darkest blacks. Aim for 500:1 or higher for more shadow detail.

Response time is the time it takes for a pixel to change color. Lower numbers are better. Accept no higher than 12 milliseconds.

Screen resolution is the number of pixels on the display. Monitor resolutions can be adjusted but flat panels work best at their native resolution (such as 1,600 by 1,200 pixels). The two monitors should have the same native resolution.

SETTING UP THE MONITOR

After you have both monitors connected to your PC, plug in both and turn them on. In Windows Vista, right-click the desktop and select Personalize. Click Display Settings. In Windows XP, click Start, then Control Panel. Double-click Display. Open the Settings tab.

In both Vista and XP, you'll see numbered boxes representing the monitors. Click Identify Monitors. A "1" appears on your primary monitor. The other monitor displays a "2." Click and drag the boxes to change the designations.

Select monitor 2 and check "Extend my windows desktop onto this monitor." Click Apply. You can then open programs and drag them between monitors.

Third-party programs improve the dual-monitor experience. UltraMon ($40) places a taskbar on each monitor. Buttons help you arrange program windows on the monitors and you can apply different wallpapers to each monitor.