Having installed my pana last weekend on a ceiling bracket,this is one tip that others might find useful ,though to all you specialists this might be obvious. Having installed the screen first ,I placed the proj on a step ladder and by measurement equallised the distance to the edges of the screen from the lens(I knew Pythagorus would come in handy one day!) I then made a final adjustment by eye. In order to locate the correct drilling point in the ceiling I next dropped a plumb line from the ceiling to the centre tripod thread on the underside of the projector. This resulted in a very accurate positioning in the ceiling of the threaded bar that I was using, to which I then attached the mounting plate which in turn was attached to the proj by the 4x4mm threaded holes. The result was perfect alignment having levelled the proj with a spirit level and no keystone adjustment. Hope this helps somebody. PS The plumb line was the idea of the guy who was helping me!