Epson PowerLite 7800p User Manual page 124

If you're mounting the projector on the ceiling and you place it above
screen level, you'll have to tilt it down to position the image on-screen.
This causes the image to lose its square shape. You can then correct
the distortion by using the function in the projector's
Keystone
menu system (see page 69) or by using the buttons on the
Keystone
projector's control panel.
If you place the projector so that the base of the lens is level with the
bottom of the screen, the image will be square and you won't have to
adjust it. If you place the lens lower than the bottom of the screen,
you'll have to tilt the projector upward if you want to fill the whole
screen with the image.
If you want to be able to control the projector's settings from a remote
computer, see Chapter 5.
You can also use the remote control to operate more than one
projector. See page 60.
Appendix A: Projector Installation
116