You guys make me laugh most of the time. In the production world where I work you may install 5 projectors in a week, all of these lines and measurement will not work. You normaly dont have 3 days to mount a projector. You should make sure the projector is installed in the center of the screen, The biggest problem I always face, is the throw angle correct and can I fix it if it is wrong. Good projectors always provide a chart which will tell you how much play you have from the projector to the top or bottom of the screen, meaning how far does it hang from the ceiling to hit the screen properly. Find a projector that allows you to adjust the up and down and side to side alignment. Note to self. Many projectors can allow for all of these adjustments, but at the expense of picture quality. Yamaha, Sony and Runco are 3 that I know will allow for adjustment with degridation of the picture unless I was a total idiot when mounting the projector. Throw distance is also a common mistake. I like to get the projector as close to the screen as I can so I dont have to expand the picture out any further than necessary. Again, the manufacturer includes a chart for this. Mounting it as close as you can will give you the best picture. I always like the electrician who has no idea where the projector is going and just installs the outlet in the corner or doesnt install one at all. It all comes with experience and after you mount the first 100 or so, you will get it.