The fictional Cube device in Cube was conceived by Dr. David W. Pravica, a mathematician. It consists of an outer cubical shell (the sarcophagus) and the inner cube. One side of the outer shell is 434 feet long. The inner cube consists of 263 = 17,576 cubical rooms (minus an unknown amount of rooms to allow for movement, as shown in the film), each having a sidelength of 15.5 feet. There is a space of 15.5 feet between the cube and the shell. Each room is labelled with three identification numbers, for example, 517 478 565. These numbers encode the starting coordinates of the room and the x, y, and z coordinates are the sums of the digits of the first, second, and third number respectively. The numbers also determine the movement of the room and the subsequent positions are obtained by cyclically subtracting the digits from one another. The resulting numbers are then successively added to the starting numbers.