Runco SC-60D 用户手册

Projector and/or screen placement — among other things — can cause geometric 
distortion in the projected image. 

To correct this, the DHD Controller provides precise, nine-point control over the projected 
image geometry. Use these controls as (and only if) needed to re-position the image 
corners, mid-points and center to eliminate “keystoning” (mis-aligned corners) or 
“pincushion” distortion (mid-points not aligned with corners). See Figure 3-21.