Webster IRP 4100 Installation Manual page 29

e To lock the plate in the desired position, rotate the knob
clockwise.
11 Repeat steps five through ten as many times as necessary to get
all edges of the projected image square and located within 0.2"
(5mm) of the frame on the IRP screen on all sides.
12 If necessary, readjust the focus and zoom on your projector.
13 If you are not able to get a satisfactory image by making these
adjustments, call PolyVision Technical Support for assistance at
1.800.620.POLY.
INSTALLING THE IRP 4500 27