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This entry explains how to fix a very common monitor problem--an incorrect aspect ratio. It is particularly useful for CRT (Cathode Ray Tube) monitors, although some LCDs (Liquid Crystal Display) may need it.
The instinctive thing to do with a new monitor, or after changing resolution, is to push the useable area all the way to the edges. Unfortunately, that can change the aspect ratio, causing squares to not be square, and circles to not be round, giving a distorted view of whatever is on the screen.
Standard monitors, using normal resolution settings (640x480, 800x600, 1024x768, 1600x1200, etc) have a 4:3 aspect ratio--width larger than height--derived from traditional TV screens, which also use CRTs.
What if the display isn't standard, or has an odd resolution? Doesn't matter--the method will work with any kind of display or aspect ratio.
Why doesn't zooming all the way out work? Monitors often don't physically match their theoretical aspect ratio, so pushing the viewable area to the edges may cause the actual ratio to be incorrect.
The adjustments are easy:
First step: Center the next graphic on a monitor. The more centered it is, the better, especially if the display isn't a flat screen or LCD. For a large, high-resolution display that needs to be more accurate for CAD or image editing, there is a bigger graphic here.
Second step: Use a ruler to measure the top and bottom. (A soft sewing tape or plastic ruler is best, to keep from scratching the screen.) The measurements should be equal. If they aren't the monitor's geometry is out of adjustment, and may involve some tinkering to get it correct. Find the "trapezoid" (sometimes called "keystone") control. It will look something like this in the monitor's menu, control bar, or manual:
Some monitors don't have this control, and may require a technician for internal adjustments.
Last step: Use the ruler to compare the top or bottom with one of the sides. If they aren't the same length, use the monitor's vertical- and horizontal-size controls until the view fills as much of the screen as possible with matching measurements. This may take a few tries.
When the adjustments are finished, there may be black bars at either the sides, or the top and bottom--very similar to a widescreen DVD viewed on a standard TV. There shouldn't be a black frame all the way around, since this indicates more useable area is available.
Parts of this FAQ were in an earlier thread: /forum/remark,7219730~mode=flat