A method and apparatus includes positioning a reactant on a surface in specific location and then directing an energy source from a device at the reactant such that it modifies the surface to either remove material or add material. The SEP may include a processor and one or more security peripherals. Ridges and grooves are alternatively provided in the side wall of each holding shaft. A delay is applied to the digitized samples during the tracking phase. The mechanism is a pump which is inside of the ball and which is operable from outside of the ball to pump ambient air into the ball. The device comprises an inflatable pouch, which can be placed under the video projector, inflating means for inflating said pouch, and deflating means for deflating said pouch, the deflating means being separate from or combined with the inflating means.