The image above has 26 shades between black and white all equidistant apart.
If you cannot see 26 distinct shades your monitor needs calibrating.
If you can see a block of black on the left hand side your monitor needs calibrating.
If you can see a block of white on the right hand side your monitor needs calibrating.
If you can see 26 distinct shades your monitor may be one of the few that does not need calibrating.
Please feel free to dowload this image to pass on to your friends and use at any time.