The images on my screen seem to shimmer or flicker and give me a headache - is there anything I can do?

The problem from the card manufacturer's point of view is that they cannot assume that you have anything beyond the bare minimum requirements for a Windows compatible display. These days that typically means 640x480 resolution, 256 colors, and a 60 Hertz refresh rate.

It's that default refresh rate that always drives me nuts.

"Refresh Rate" is, to over-simplify, the number of times each second that the video card draws an image of your screen on the monitor. That's typically much faster than you or I might notice. But it's slow enough that as you look at your monitor, especially if you look from side to side, you might notice a bit of flickering.

Depending on the capabilities of your monitor and video card you can probably change your refresh rate to something else. Most video cards and monitors support settings other than 60hz. And it doesn't take much of a change to make the flicker go away.

To change your monitor's refresh rate in Windows XP:

• Right-click anywhere on your desktop.

• Select Properties.

• Select the Settings tab.

• Click the Advanced button.

• Click on the Monitor tab.

• Click on the Screen refresh rate drop-down list for the settings that you have available to you.

• Select a new refresh rate if you like, and press OK. Your system will try the new rate and give you 15 seconds to approve it. If your screen goes completely nuts, do nothing. After 15 seconds without a response from you the old settings will be restored.

Just about anything higher than 60hz is enough to reduce or eliminate visible flicker. 72hz or 75hz seem popular and commonly available options.

What if 60hz is the only option listed? Well, there are three possibilities:

• You have a very old or perhaps very cheap display adapter - this is unlikely these days.

• You have the default VGA video driver installed. If you locate and install the video drivers for your specific video card you should have access to all the features that card has to offer, including different refresh rates.

• You have an LCD screen. LCD screens typically operate at only 60hz. But the good news is that the technology is sufficiently different that flicker at 60hz should simply not be an issue.

Finally, the limits of your ability to view video are typically due to your monitor. A monitor that claims to be capable of displaying, say, 1600x1200 may be able to do so but not with a crisp image. Set the resolution as high as you can see comfortably, but no higher. Slightly fuzzy images, like flicker, can cause eyestrain and give you a headache.