Holo-tanks were devices which projected a holographic image which gave the viewer the impression of being "in" the image. It was a three-dimensional visual projection area resembling a small amphitheater. The holo-tank was completely circular and recessed below the level of the floor. Observers stood around its outer edge and looked into it. Holo-tanks were primarily employed in military command centers to observe tactical movements. Targets were displayed as points of light and located in a true, scaled-down position with respect to some reference point. A three-dimensional grid system, that was superimposed over the holo-tank projection field of regard, allowed for the easy location of targets.