This image is to check the linearity of the display device. That's a fancy way to say "Is the middle of the picture in the middle of the screen?"

The center circle should be round, not egg-shaped. The lines from corner to corner should be straight. The small edge-locate circles along the edges are so you can tell if you are seeing all the way to the edge of the image. (In other words, see if the screen is cutting of the edge of the image.)

General purpose.

Lots of goodies here. Along the right side is a "rainbow" with all the possible colors. Along the sides are the edge-locate circles again. The large color sqares in the black area are RGB pure colors - useful to determine if a color is missing. If there is one missing, that square will be black. The color squares in the white are "cyan", "magenta" and "yellow". Printers usually use these colors rather than RGB. Then there are the thin, vertical lines in the center. These can be used to see if any of the colors are misaligned. A common cause would be different length cables for at least one of the channels.

To check black, white, and the levels of grey.

The numbers are "percent of full white". Thus "90" means "90% of true white" or "just a little darker than true white". Ideal would be for you to be able to see the difference between "0" and "2" and see the difference between "98" and "100". If you are checking out a projector, you probably won't be able to. So, use the brightness, contrast, and gamma to change the way the image looks. On a projector, you will probably lose a couple black squares and a couple white squares. There is no gamma applied to the log scale.