Do the patches marked 0 and 10 in the grayscale appear to be the same? If they do then you need to calibrate your monitor black point. Do the patches marked 95 and 100 appear to be the same? If they do then you need to calibrate your monitor white point. If the patches have a color tint, you can correct problem by calibrating monitor gamma for each color channel individually.
Stand ten feet from your monitor and examine the above figure. If the smooth patch is darker or lighter than the background then you need to calibrate monitor gamma.
Many computer monitors come from the factory preset for an office working environment which may not be ideal for viewing and editing photographic images. For color accuracy and consistency work in a darkened environment.
You can calibrate black and white points without any special software. To adjust monitor gamma you'll need special software such as QuickGamma. QuickGamma is free software based on Norman Koren's gamma and black level chart.
It takes just a few minutes to make these adjustments. As a reward you will view images on the web as they were designed to be viewed. If you're a web designer, or share images with others, then it's imperative that you calibrate your system to a standard. For the web or email use the sRGB standard.
The sRGB standard specifies a color temperature of 6500°. Most monitors have provisions for setting color temperature using on-screen menus. Be sure to set monitor color temperature before calibration. Also check that your display is configured for 24 or 32-bit color. With 16-bit color there is not enough color depth to calibrate properly. Let your monitor warm-up for at least 15 minutes before calibration.
For instructions on calibrating your printer visit Photoshop for Photographers and click on Introduction > Calibration.