HP mp3220 series User Manual page 17

Setting Up
Calculating projection dimensions
distance from lens to screen = A × width of screen
minimum and maximum distance from screen = B
width of screen = 0.8 × diagonal of screen (for 4:3 screen)
projector lens below bottom of screen = C × width of screen (for 4:3 screen)
A = 2.0 to 2.4
B = 1.2 to 12 m (4 to 40 ft)
C = 0.11 to 0.42
To set up on a table
User's Guide 17