You can project an evenly rectangular image by placing the projector directly in front of the center of the screen and keeping it level. If you place the projector at an angle to the screen, or tilted up or down, or off to the side, you may need to correct the image shape for the best display quality.
When you turn on automatic keystone correction in your projector's Settings menu, your projector automatically corrects keystone effects when you reposition the projector.
You can also press the 
Auto Keystone button to
automatically correct horizontal and vertical keystoning.