Often on photography websites you can find a table with different shades of gray, from all-white to all-black.
Why do you need such a table?
MONITOR TEST CHART
This table is to check if your monitor is set up properly.
If your monitor is poorly set up - too dark, too light, or the contrast is not set properly, you will not be able to view photos correctly.
One of the purposes of monitor calibration is to ensure that shades that are slightly lighter than black are different from full black and shades that are slightly darker than white are different from full white.
The scale above shows 26 shades of gray from full black to full white.
Below are two circles that enclose four circular segments of different shades each. You should be able to see all four, up to the smallest circle in the center in both circles.
Image to check monitor adjustment and calibration
On a well-calibrated monitor, no color should blend in with the previous one. This can be achieved by adjusting the brightness and contrast on your monitor.
For more accurate calibration, hardware methods are used - this is when a special color analyzer is attached to your monitor and, after detailed analysis, makes the necessary adjustments to the settings independently.
Click here for links to instructions on how to calibrate your monitor: