In the 14th century, a blacksmith called Masamune developed a two-layer structure of soft and hard steel for use in swords. Source: Internet
It uses a two-layer grid of electrodes to measure finger movement: one layer has vertical electrode strips that handle vertical movement, and the other layer has horizontal electrode strips to handle horizontal movements. Source: Internet
This method has many advantages over sending a single large file: *The two-layer compression could sometimes achieve almost a tenfold improvement over the original DVD/CD image. Source: Internet