Equilibrium, also known as "Equi-librium" is an interlocking puzzle in the shape of a sphere. Copyrighted in 1974 by Reiss Games, Inc., it consists of 6 closed arch pieces, 5 of which have pegs on their straight center. The two pegs block the other pieces from being shifted back or forth, only the sixth piece is different having only one peg and two notches. These notches are above and below where the peg would be located on the other pieces, allowing only this notched piece to be moved at first. When it is moved so the notch fits over another piece's peg, the two pegged piece can be moved. Once a two peg piece has been slid to the side, the notched piece can be moved to its second notch and lifted off. Once the notch piece is removed, all the others become loose and the puzzle usually crumbles into its remaining pieces. The challenge is to put it back together. Equilibrium was sold in a cardboard box, with a solution sheet enclosed."It looks tranquilizing till you take it... apart, that is. But getting this well-designed sphere back together again won't be easy."