and 7 to 10 track 90 initially slopes slightly upwardly towards the rear of the enclosure and then dips slightly at an angle below the horizontal curved track 91 slopes sharply upwardly towards the top of portion 15 with the intersection of tracks 90 and 91 defining an indentation or cavity 94 track 91 may be straight but the use of a curvature facilitates insertion as the cart is pushed into the enclosure forward rollers 85 are picked up by tracks 90 to precisely center the projector within the enclosure as insertion of the cart continues forward rollers 85 engage tracks 91 and 92 fig9 to initiate rapid tilting while at the same time trailing rollers 85 engage track 90 when fully inserted trailing rollers 85 come to rest in cavity 94 and the projector will be correctly and precisely positioned within the enclosure for projection of images onto mirror 9 and screen 11 moreover as tracks 90 are angled slightly upwardly casters 56 and the entire cart assembly will be elevated above floor level so that the full weight of the cart and projector is transferred to the tracks and the enclosure 39 s side walls this ensures registration of the projector relative to the enclosure regardless of irregularities in the underlying floor the lower edges of the.