BenQ LW650 User Manual page 16

For example, if you are using a 100-inch screen, the recommended projection distance is 2933
mm.
If your measured projection distance is 2000 mm, the closest match in the
(mm)" column is 2053 mm. Looking across this row shows that a 70'' (about 1.8 m) screen is
required.
To optimize your projection quality, we suggest doing the projection by referring to the values listed in the
non-gray rows.
The values in the gray cells are for reference only.
All measurements are approximate and may vary from the actual sizes.
BenQ recommends that if you intend to permanently install the projector, you should physically test the
projection size and distance using the actual projector in situ before you permanently install it, so as to
make allowance for this projector's optical characteristics. This will help you determine the exact mounting
position so that it best suits your installation location.
16 Positioning your projector
"Projection distance