To get an optimal view of graphics on the Web, your screen
should not be too dark or too light nor should it have a color cast to it.
There should be twenty equal segments above, including black and white.
To adjust your monitor to the correct gamma - adjust your monitor contrast to get separation between the black and dark grey on the left (you should see separation between the two last dark tones on the left).
Then adjust the white by creating a separation between the light grey and white on the right (you should see separation between the two light tones on the right).
Lastly, look for any color cast in the white and grey tones - they should be neutral in color. Monitors tend to have a magenta cast to them until they have warmed-up for 30 minutes.