Digi-Comp II topic

The Digi-Comp II was a toy computer manufactured by E.S.R., Inc. that used marbles rolling down a ramp to perform basic calculations. A two-level masonite platform with guides served as the medium for a supply of marbles that rolled down an inclined plane moving plastic cams as they went. The plastic cams played the part of flip-flops in an electronic computer - as a marble passed one of the cams, it would flip the cam around - in one position, the cam would allow the marble to pass in one... full article at wikipedia