“This is the fundamental difference between digital and analog: A digital valve is either on or off; an analog valve, like your kitchen faucet, can be anything in between. In the hydraulic computer, all that is required of the input signal is that it be strong enough to move the valve. In this case, the difference that makes a difference is the difference in water pressure sufficient to switch the valve on. And since a weakened signal entering an input will still produce a full-strength output, we can connect thousands of layers of logic, the output of one layer controlling the next, without worrying about a gradual decrease in pressure. The output of each gate will always be at full pressure.”