1. A FLUID OPERATED UNIVERSAL LOGICAL DEVICE CAPABLE OF ADJUSTABLY PERFORMING A PLURALITY OF DIFFERENT LOGICAL FUNCTIONS, AND ADJUSTED TO PERFORM AS A LOGICAL HALF ADDER TO PRODUCE AN OUTPUT MANIFESTIVE OF CARRY ONLY IN THE BINARY ADDITION OF THREE BINARY DIGIT INPUTS IN ACCORDANCE WITH THE LAWS OF BINARY ADDITION COMPRISING: (A) A FIRST FLUID INPUT DUCT HAVING FLUID THEREIN AT THE HIGHER OF TWO PREDETERMINED PRESSURE LEVELS; (B) A SECOND FLUID INPUT DUCT HAVING FLUID THEREIN AT A SELECTED ONE OF SAID TWO PRESSURE LEVELS TO MANIFEST THE BINARY DIGITAL VALUE OF A FIRST DIGIT TO BE ADDED, WHEREIN HIGH PRESSURE MANIFESTS A BINARY "1" AND LOW PRESSURE BINARY "0"; (C) A THIRD FLUID INPUT DUCT HAVING FLUID THEREIN AT THE LOWER OF THE TWO PREDETERMINED PRESSURE LEVELS; (D) A FIRST TWO-POSITION VALVE HAVING FIRST AND SECOND FLUID OUTLET DUCTS, AND FIRST, SECOND, AND THIRD FLUID INLET PORTS, RESPECTIVELY CONNECTED TO SAID FIRST, SECOND AND THIRD FLUID INPUT DUCTS, AND OPERATIVE IN A FIRST OF SAID TWO POSITIONS TO CONNECT SAID FIRST FLUIDOUTLET DUCT TO SAID SECOND FLUID INLET PORT, AND SAID SECOND FLUID OUTLET DUCT TO SAID THIRD FLUID INLET PORT, AND IN A SECOND OF SAID TWO POSITIONS TO CONNECT SAID FIRST FLUID OUTLET DUCT TO SAID FIRST FLUID INLET PORT, AND SAID SECOND FLUID OUTLET DUCT TO SAID SECOND FLUID INLET PORT, THE SAID FIRST POSITION OF SAID VALVE MANIFESTING A BINARY "0" DIGITAL INPUT AND THE SAID SECOND POSITION MANIFESTING A BINARY "1" DIGITAL INPUT; (E) A SECOND TWO-POSITION VALVE HAVING A SINGLE FLUID OUTPUT DUCT, AND FIRST AND SECOND FLUID INLET PORTS RESPECTIVELY CONNECTED TO THE SAID FIRST AND SECOND FLUID OUTLET DUCTS OF SAID FIRST VALVE, AND OPERATIVE IN A FIRST OF SAID TWO POSITIONS TO CONNECT SAID OUTPUT DUCT TO SAID SECOND INLET PORT, AND IN A SECOND OF SAID TWO POSITIONS TO CONNECT SAID OUTLET DUCT TO SAID FIRST INLET PORT, THE SAID FIRST POSITION OF SAID VALVE MANIFESTING A BINARY "0" AND THE SECOND POSITION MANIFESTING A BINARY "1" DIGITAL INPUT; (F) AND FLUID OPERATED MEANS FOR SELECTIVELY ESTABLISHING SAID FIRST AND SAID SECOND VALVES IN ONE OF THEIR TWO POSITIONS TO MANIFEST THE RESPECTIVE BINARY DATA INPUTS; WHEREBY SAID OUTPUT DUCT WILL BE CONNECTED TO HIGH PRESSURE FLUID IN SAID INPUT DUCTS TO MANIFEST A BINARY "1," OR TO LOW PRESSURE FLUID IN SAID FLUID INPUT DUCTS TO MANIFEST A BINARY "0" CARRY ONLY AS A FUNCTION OF THE THREE DIGITS TO BE ADDED.