for most installations, the lens surface of the projector is parallel to the screen—this prevents major keystoning of the image (i.e., an image with non-parallel sides). in addition, the projector must be kept level from side-to-side in order for the lamp to function safely. to make small corrections to the projector's level, rotate each leg as necessary to raise or lower. see figure 2.39. for angled installations, see “special mounting” under 2.3, projector position and mounting earlier in this section.