Check out http://pruned.blogspot.com/2012/01/gardens-as-crypto-water-computers.html http://pruned.blogspot.com/2012/01/gardens-as-crypto-water-c... to see a Sov

Check out http://pruned.blogspot.com/2012/01/gardens-as-crypto-water-computers.html http://pruned.blogspot.com/2012/01/gardens-as-crypto-water-c... to see a Soviet water-based computer. I don't know the details of it, but it appears to be able to solve PDE's by mapping the PDE you're solving to a hydraulic system. Since the flow of water is governed by PDEs, once you've mapped the problem to the computer you can just make some analog measurements of water flow to get the answer you're looking for. (Is this right?) I have to wonder, thought, whether this is can really be called a computer. If you do, don't you also have to consider a simple integrator circuit one? Error correction must also be somewhere between a total PITA and impossible, right?