You should see 24 different gradations in the above image
ranging from 100% grey (black) on the left to 0% grey (white) on the right.
You should be able to distinguish the differences between each
of the gradations, If you can not clearly distinguish the differences
please adjust your monitor.
Using your monitors brightness control adjust it such that the
left-most block is black, but still distinguishable from the next gradation. Then using your monitors contrast control adjust it such that the right-most
block is white, but still distinguishable from the next gradation.
Make sure the mid-tone gradations are grey, if the RGB (Red, Green, Blue)
balance of your monitor is off they might appear to have a coloration.
By carefully calibrating your monitor you guarantee
that you see the photographs as they were meant to be seen.