The idea for this puzzle comes from Jerry Slocum and Jack Botermans "New Book of Puzzles," and dates from the 1930's. The object is to get all 4 sides to add up to 555, the height of the Washington Monument! Each of the cubes will rotate on the internal post. A great challenge for the math inclined as it is VERY difficult. It might make a good class project from middle school to high school. Puzzle fan Ken Irvine has done an interesting analysis of this puzzle: turns out there are over 262,000 possible permutations of the disks. There are only 9 possible solutions.