Attached Link: http://www.easyrgb.com/index.html

Every monitor has a different color and brightness profile, and those profiles change over time, like layingback wrote. Professionals often use calibration tools, not only to get the best possible image on their monitors, but also to get consistent results. These calibration tools, including spectrometers, can be quite expensive. There's also a range of online calibration tools. They're not as sophisticated and accurate as the professional tools, but they certainly help to set up your monitor better than the factory defaults. They can help you create images that have the brightness and contrast that you intend it to have, and if a viewer has calibrated his/her monitor too, the viewer will see (almost) the same brightness/contrast you do. I've calibrated all my monitors using the online tool in the link below, and images look (almost) the same on all my monitos.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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