Set up your room environment
A low room light level is important to achieving useful results.
In the daytime, close window blinds or curtains to block daylight from the room.
Turn off overhead lighting. You may keep a small table lamp turned on, for example with a 40 watt bulb, but the light from this lamp should not shine directly on the display.
If you have a light meter, an ambient room lighting level of 20 Lux or lower is appropriate for the test environment.
Adjust your monitor
The set of controls that affect black level will vary depending on the monitor type and model.
If your monitor has a Picture Mode setting, choose "Movie" mode to provide the greatest dynamic range in your darkened room environment.
Then adjust Brightness so that the background of this page appears black, not dark gray. Depending on the monitor, the Brightness setting may or may not cause the darkest checkerboards above to disappear.
Check the black level
The ideal black level setting is when you can just barely see the upper left checkerboard.
Depending on what settings are available with your monitor you may or may not be able to control its visibility.
If you can vary the Brightness setting and make the upper left checkerboard disappear and reappear, then adjust to make it barely visible.