SOS Automatic Decompression Computer
One of the earliest dive computers was the SOS Automatic Decompression Computer; affectionately referred to as the “Bend-o-matic”. This computer was a fully mechanical analogue computer. It had a balloon that was connected via a porous ceramic block to a sealed metal chamber with the needle indicating pressure inside the chamber. As the diver descended the balloon was compressed forcing gas through the porous block into the chamber. The deeper you went and the longer you were under pressure the more gas got forced through the ceramic block. As you ascended the excess pressure in the sealed container tried to equalize the pressure in the balloon and so the needle went back down.
One can consider it as a single tissue computer unlike the eight or sixteen tissue electronic computers used today!