Eight is the second smallest cube number (after 13): 8 = 23 = 2 × 2 × 2. A queen or king in chess can move in eight different directions, in the same way that a compass has eight principal points: north, northeast, east, southeast, south, southwest, west, and northwest. In three dimensions, there are eight diagonal ways to move, corresponding to the eight octants into which three-dimensional space is divided by three mutually-perpendicular planes. Add a fourth dimension and movement becomes possible back and forth along four directions at right angles to each other: up and down, left and right, forward and back, and one other! The Spanish dollar was a gold coin with a value of eight reale, and was sometimes actually cut into eight wedge-shaped pieces – "pieces of eight" – to make change.