There is one big omission in this article, which seems to focus mainly on hydrodynamic computing: "static" hydraulic computing, as implemented with relay valves --- and found major application as the control unit of passenger car automatic trnsmissions throughout much of the last century, before electronic controls became common. Examples:<p><a href="http://cogpro.com/chapters/M-ThreeSpeedHydramatic/images/M%20-%203%20spd%20HM0092_jpg.jpg" rel="nofollow">http://cogpro.com/chapters/M-ThreeSpeedHydramatic/images/M%2...</a><p><a href="http://oldcarblog.com/manuals/1970/1970%20Service%20Manual/19-%20400%20Turbo%20AT/b_P0018.jpg" rel="nofollow">http://oldcarblog.com/manuals/1970/1970%20Service%20Manual/1...</a>