QuickGamma is probably the most economical way to accurately calibrate your monitor.  It is free for personal use with donations welcomed. I have personally compared calibrating my monitor with the X-rite  Color Munki, for which I paid more than $400, to calibrating with Quickgamma and can tell no discernible difference between the two methods.  (Note: Results may differ with different monitors) Download QuickGamma from the Quickgamma website.  I personally recommend the Google link. Using Softpedia, if your are not careful, will also install other software which you may not want. After installing QuickGamma be sure to read the entire help section of the program.  It contains important information and shouldn’t take more than five or ten minutes. Once you are done reading watch the video below as it has an excellent tutorial of the step by step calibration process. (Note: Both images on the left may copied and used freely for both private and business use.  The chart, upper left, is a free royalty free image and the test image below the chart is in the public domain.  Right click image and “Save image as..” to download to your computer.)
You should see a definitive difference between each of the 11 levels in the gray-scale chart above and if your monitor is exceptionally good you should also see a faint circle in #1 and #11.  Make sure your browser window size is set to 100% and sit back about 4 feet from your screen. Each of the color boxes should be nearly uniform in tone. If half of the a box is lighter or darker you need to calibrate your monitor. 
The test image above is also useful for checking your monitor. You should be able to see detail in all of the areas including the shadows.
Click Image to enlarge
Click Image to enlarge
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