Another place where memory storage was needed was for entertainment purposes: the cylinders and punched disks that operate music boxes, and also the punched paper rolls in player pianos. There was an almost infinite variety of these devices, including some automata programmed by large wooden cylinders with metal pins. I’ve collected some things along these lines but I’ve been more interested in devices directly associated with computing. One very interesting technology that I found recently is cam memory. One example that I really like contains information on how to adjust from the local compass reading anywhere on the earth’s surface to true magnetic north. The memory storage unit consists of a very lopsided cylinder of aluminum that is actually a map of the earth. At first when I saw it I thought the device had been smashed, but when you look at it closely, you realize it’s been carefully machined. There’s a stylus that can be run along the axis of the cylinder, much like a phonograph needle, that reads the radius at any point around the surface. It’s this radius that encodes the deviation of the local magnetic field. It’s quite a beautiful object. There were also computational devices in aircraft navigation systems—you can still occasionally find these in electronics swap meets and junk yards—that have ball disc and roller integrators, which were able to mechanically monitor a plane’s direction and speed and translate that into latitude and longitude. Those are pretty amazing, and I’m sure were extremely costly to produce. Of course, you can do all that now with a few lines of computer code.