220.png
http://www.obiektywni.pl/czytelnia/artykul-204-2.php


650px-Gammatest.svg.png
To see whether your computer monitor is properly hardware adjusted
and can display shadow detail in sRGB images properly, you should
see the left half of the circle in the large black square very
faintly (or not at all), but the right half should be clearly visible.
If not, you can adjust your monitor's contrast and/or brightness
setting. This alters the monitor's perceived gamma. The image is best
viewed against a black background.


Gamma_black_new.png
http://www.normankoren.com/makingfineprints1A.html
This chart features gradual density changes along horizontal scan lines
(thus eliminating risetime problems). It allows more precise gamma
estimation than most traditional charts. I encourage you to download
it and check it occasionally. 


monitor_test_txt22.png
http://www.normankoren.com/makingfineprints1A.html
The patterns on the right represent an ultimate test of monitor quality
and calibration. If your monitor is functioning properly and calibrated
to gamma = 2.2 or 1.8, the corresponding pattern will appear smooth
neutral gray when viewed from a distance. Any waviness, irregularity,
or color banding indicates incorrect monitor calibration or poor performance.
You will see irregularities if the black level (brightness control) is
set too low, causing dark areas clip, if the monitor saturates in bright
areas (a sign of old age), or if your monitor is malfunctioning in any way.
The optimum black level settng is typically a little higher than the lowest
level where smoothness can be achieved. This setting should be consistent
with the gamma chart instructions, above.